Add support for some ES proposals that we use (#43)

config/babel.dev.js

@@ -15,6 +15,8 @@ module.exports = {
     'babel-preset-react'
   ].map(require.resolve),
   plugins: [
+    'babel-plugin-syntax-trailing-function-commas',
+    'babel-plugin-transform-class-properties',
     'babel-plugin-transform-object-rest-spread'
   ].map(require.resolve)
 };