Rails app stopped running locally after pushing it to Heroku master - ruby-on-rails

Question

I pushed a (very simple) Rails app up to Heroku, the build was successful and it works online (minus some route issues), but now I can't get it to run locally. It's actually a clone of the "getting started" app I thought I'd modify to avoid deployment issues. When I try to start a Rails server I get the following message:
$ rails s
Looks like your app's ./bin/rails is a stub that was generated by Bundler.
In Rails 4, your app's bin/ directory contains executables that are versioned
like any other source code, rather than stubs that are generated on demand.
Here's how to upgrade:
bundle config --delete bin # Turn off Bundler's stub generator
rake rails:update:bin # Use the new Rails 4 executables
git add bin # Add bin/ to source control
You may need to remove bin/ from your .gitignore as well.
When you install a gem whose executable you want to use in your app,
generate it and add it to source control:
bundle binstubs some-gem-name
git add bin/new-executable
Bundler::GemRequireError: There was an error while trying to load the gem 'uglifier'.
Gem Load Error is: Could not find a JavaScript runtime. See https://github.com/rails/execjs for a list of available runtimes.
Backtrace for gem load error is:
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/execjs-2.7.0/lib/execjs/runtimes.rb:58:in `autodetect'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/execjs-2.7.0/lib/execjs.rb:5:in `<module:ExecJS>'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/execjs-2.7.0/lib/execjs.rb:4:in `<main>'
org/jruby/RubyKernel.java:961:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `block in require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:240:in `load_dependency'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/uglifier-3.2.0/lib/uglifier.rb:1:in `<main>'
org/jruby/RubyKernel.java:961:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/uglifier-3.2.0/lib/uglifier.rb:5:in `block in (root)'
org/jruby/RubyArray.java:1734:in `each'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler/runtime.rb:1:in `block in (root)'
org/jruby/RubyArray.java:1734:in `each'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler/runtime.rb:82:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler/runtime.rb:77:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler/runtime.rb:66:in `<main>'
org/jruby/RubyKernel.java:961:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler.rb:108:in `block in require'
org/jruby/RubyKernel.java:1747:in `tap'
C:/blog/config/application.rb:7:in `(root)'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:1:in `(root)'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:78:in `<main>'
org/jruby/RubyKernel.java:961:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:75:in `block in server'
org/jruby/RubyKernel.java:1298:in `loop'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands.rb:17:in `<main>'
org/jruby/RubyKernel.java:961:in `require'
C:/jruby-9.1.12.0/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:54:in `require'
C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/app_rails_loader.rb:1:in `<main>'
org/jruby/RubyKernel.java:979:in `load'
C:/jruby-9.1.12.0/bin/rails:22:in `<main>'
Bundler Error Backtrace:
block in require at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler/runtime.rb:85
each at org/jruby/RubyArray.java:1734
block in require at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler/runtime.rb:77
each at org/jruby/RubyArray.java:1734
require at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler/runtime.rb:66
require at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/bundler-1.15.3/lib/bundler.rb:108
<main> at C:/blog/config/application.rb:7
require at org/jruby/RubyKernel.java:961
block in (root) at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:1
tap at org/jruby/RubyKernel.java:1747
server at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:78
server at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:75
<main> at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:39
require at org/jruby/RubyKernel.java:961
block in (root) at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/commands.rb:17
loop at org/jruby/RubyKernel.java:1298
(root) at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/app_rails_loader.rb:1
<main> at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/app_rails_loader.rb:45
require at org/jruby/RubyKernel.java:961
require at C:/jruby-9.1.12.0/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:54
<main> at C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/railties-4.2.4/lib/rails/app_rails_loader.rb:34
load at org/jruby/RubyKernel.java:979
<main> at C:/jruby-9.1.12.0/bin/rails:22
Removing uglifier and coffee-rails gets the app up and running locally so, I tried that and followed the upgrade instructions, then used bundle install to add them again, with the same result. I also can't push a version of this app up to Heroku without those gems so I'm left scratching my head where to go from here.
Here is a copy of the app I pushed to Git (excuse the language on one of the commits I was quite frustrated) to help with trouble shooting
https://github.com/taswelldavis/blog
Thanks for the help,
Anna