rails application not deploying to heroku (application error message) - ruby-on-rails

Question

I am trying to deploy a simple hello world Rails application to Heroku but am getting an application error. The weird thing is it worked fine for my other Rails application but it doesn't work for this one even though I made the same changes to both, including having the same Gemfile, controller action and root route. It works fine locally but not when I deploy it.
http://calm-oasis-3599.herokuapp.com/
This is the error output when I run heroku run rails console and heroku logs.
Any help with finding out why I am getting this error is greatly appreciated.
Here's my Gemfile.lock:
GEM
remote: https://rubygems.org/
specs:
actionmailer (4.2.4)
actionpack (= 4.2.4)
actionview (= 4.2.4)
activejob (= 4.2.4)
mail (~> 2.5, >= 2.5.4)
rails-dom-testing (~> 1.0, >= 1.0.5)
actionpack (4.2.4)
actionview (= 4.2.4)
activesupport (= 4.2.4)
rack (~> 1.6)
rack-test (~> 0.6.2)
rails-dom-testing (~> 1.0, >= 1.0.5)
rails-html-sanitizer (~> 1.0, >= 1.0.2)
actionview (4.2.4)
activesupport (= 4.2.4)
builder (~> 3.1)
erubis (~> 2.7.0)
rails-dom-testing (~> 1.0, >= 1.0.5)
rails-html-sanitizer (~> 1.0, >= 1.0.2)
activejob (4.2.4)
activesupport (= 4.2.4)
globalid (>= 0.3.0)
activemodel (4.2.4)
activesupport (= 4.2.4)
builder (~> 3.1)
activerecord (4.2.4)
activemodel (= 4.2.4)
activesupport (= 4.2.4)
arel (~> 6.0)
activesupport (4.2.4)
i18n (~> 0.7)
json (~> 1.7, >= 1.7.7)
minitest (~> 5.1)
thread_safe (~> 0.3, >= 0.3.4)
tzinfo (~> 1.1)
arel (6.0.3)
binding_of_caller (0.7.2)
debug_inspector (>= 0.0.1)
builder (3.2.2)
byebug (8.2.0)
coffee-rails (4.1.0)
coffee-script (>= 2.2.0)
railties (>= 4.0.0, < 5.0)
coffee-script (2.4.1)
coffee-script-source
execjs
coffee-script-source (1.10.0)
debug_inspector (0.0.2)
erubis (2.7.0)
execjs (2.6.0)
globalid (0.3.6)
activesupport (>= 4.1.0)
i18n (0.7.0)
jbuilder (2.3.2)
activesupport (>= 3.0.0, < 5)
multi_json (~> 1.2)
jquery-rails (4.0.5)
rails-dom-testing (~> 1.0)
railties (>= 4.2.0)
thor (>= 0.14, < 2.0)
json (1.8.3)
loofah (2.0.3)
nokogiri (>= 1.5.9)
mail (2.6.3)
mime-types (>= 1.16, < 3)
mime-types (2.6.2)
mini_portile (0.6.2)
minitest (5.8.2)
multi_json (1.11.2)
nokogiri (1.6.6.3)
mini_portile (~> 0.6.0)
pg (0.17.1)
rack (1.6.4)
rack-test (0.6.3)
rack (>= 1.0)
rails (4.2.4)
actionmailer (= 4.2.4)
actionpack (= 4.2.4)
actionview (= 4.2.4)
activejob (= 4.2.4)
activemodel (= 4.2.4)
activerecord (= 4.2.4)
activesupport (= 4.2.4)
bundler (>= 1.3.0, < 2.0)
railties (= 4.2.4)
sprockets-rails
rails-deprecated_sanitizer (1.0.3)
activesupport (>= 4.2.0.alpha)
rails-dom-testing (1.0.7)
activesupport (>= 4.2.0.beta, < 5.0)
nokogiri (~> 1.6.0)
rails-deprecated_sanitizer (>= 1.0.1)
rails-html-sanitizer (1.0.2)
loofah (~> 2.0)
rails_12factor (0.0.2)
rails_serve_static_assets
rails_stdout_logging
rails_serve_static_assets (0.0.4)
rails_stdout_logging (0.0.4)
railties (4.2.4)
actionpack (= 4.2.4)
activesupport (= 4.2.4)
rake (>= 0.8.7)
thor (>= 0.18.1, < 2.0)
rake (10.4.2)
rdoc (4.2.0)
json (~> 1.4)
sass (3.4.19)
sass-rails (5.0.4)
railties (>= 4.0.0, < 5.0)
sass (~> 3.1)
sprockets (>= 2.8, < 4.0)
sprockets-rails (>= 2.0, < 4.0)
tilt (>= 1.1, < 3)
sdoc (0.4.1)
json (~> 1.7, >= 1.7.7)
rdoc (~> 4.0)
spring (1.4.3)
sprockets (3.4.0)
rack (> 1, < 3)
sprockets-rails (2.3.3)
actionpack (>= 3.0)
activesupport (>= 3.0)
sprockets (>= 2.8, < 4.0)
sqlite3 (1.3.11)
thor (0.19.1)
thread_safe (0.3.5)
tilt (2.0.1)
turbolinks (2.5.3)
coffee-rails
tzinfo (1.2.2)
thread_safe (~> 0.1)
uglifier (2.7.2)
execjs (>= 0.3.0)
json (>= 1.8.0)
web-console (2.2.1)
activemodel (>= 4.0)
binding_of_caller (>= 0.7.2)
railties (>= 4.0)
sprockets-rails (>= 2.0, < 4.0)
PLATFORMS
ruby
DEPENDENCIES
byebug
coffee-rails (~> 4.1.0)
jbuilder (~> 2.0)
jquery-rails
pg (= 0.17.1)
rails (= 4.2.4)
rails_12factor (= 0.0.2)
sass-rails (~> 5.0)
sdoc (~> 0.4.0)
spring
sqlite3
turbolinks
uglifier (>= 1.3.0)
web-console (~> 2.0)
BUNDLED WITH
1.10.6
Here's the spring gem file
#!/usr/bin/env ruby
# This file loads spring without using Bundler, in order to be fast.
# It gets overwritten when you run the `spring binstub` command.
unless defined?(Spring)
require 'rubygems'
require 'bundler'
if (match = Bundler.default_lockfile.read.match(/^GEM$.*?^ (?: )*spring \((.*?)\)$.*?^$/m))
Gem.paths = { 'GEM_PATH' => [Bundler.bundle_path.to_s, *Gem.path].uniq }
gem 'spring', match[1]
require 'spring/binstub'
end
end

Answer 1

You may not need to include spring under test group as seen here
Keep it under the development group alone.
Also the version of spring in your gemlock is 1.4.3 and heroku is complaining about 1.4.2. Maybe you need to explicitly specify a version in your gemfile, delete your Gemfile.lock(which should not always happen), run bundle again, commit your changes and redeploy.