Enable cache for babel-loader (#4505)

.travis.yml

@@ -6,6 +6,7 @@ cache:
   - node_modules
   - public/assets
   - public/packs-test
+  - tmp/cache/babel-loader
 dist: trusty
 sudo: required
 

config/webpack/loaders/babel.js

+const { resolve } = require('path');
+
 module.exports = {
   test: /\.js$/,
   // include react-intl because transform-react-remove-prop-types needs to apply to it
@@ -8,5 +10,6 @@ module.exports = {
   loader: 'babel-loader',
   options: {
     forceEnv: process.env.NODE_ENV || 'development',
+    cacheDirectory: resolve(__dirname, '..', '..', '..', 'tmp', 'cache', 'babel-loader'),
   },
 };