How do I fix this webpack deploy error on heroku? - ruby-on-rails

Question

When trying to deploy a react_on_rails app to heroku. I get a series of the following errors. Everything works fine locally, however when I try to deploy to heroku I get:
ERROR in ./app/bundles/appbundle/startup/MyApp.jsx
remote: Module not found: Error: Cannot resolve 'file' or 'directory' /tmp/build_5f0499a33a66627b6911c88bcf69f8ab/client/node_modules/react in /tmp/build_5f0499a33a66627b6911c88bcf69f8ab/client/app/bundles/appbundle/startup
The error seems straight forward, but I don't understand why it is not finding the files. It finds them perfectly fine on my local machine, so I don't understand what is wrong.
const webpack = require('webpack')
const path = require('path')
const glob = require('glob')
const devBuild = process.env.NODE_ENV !== 'production'
const nodeEnv = devBuild ? 'development' : 'production'
const config = {
entry: [
'es5-shim/es5-shim',
'es5-shim/es5-sham',
'babel-polyfill'
].concat(glob.sync('./app/bundles/**/startup/*')),
output: {
filename: 'webpack-bundle.js',
path: '../app/assets/webpack'
},
resolve: {
extensions: ['', '.js', '.jsx'],
alias: {
react: path.resolve('./node_modules/react'),
'react-dom': path.resolve('./node_modules/react-dom')
}
},
plugins: [
new webpack.DefinePlugin({
'process.env': {
NODE_ENV: JSON.stringify(nodeEnv)
}
})
],
module: {
loaders: [
{
test: require.resolve('react'),
loader: 'imports?shim=es5-shim/es5-shim&sham=es5-shim/es5-sham'
},
{
test: /\.jsx?$/,
loader: 'babel-loader',
exclude: /node_modules/
}
]
}
}
module.exports = config
if (devBuild) {
console.log('Webpack dev build for Rails') // eslint-disable-line no-console
module.exports.devtool = 'eval-source-map'
} else {
config.plugins.push(
new webpack.optimize.DedupePlugin()
)
console.log('Webpack production build for Rails') // eslint-disable-line no-console
}