Attempt to fix Travis CI issue.

Based on vuejs/vue-cli#3678 (comment)

Author: gaurav

babel.config.js

@@ -1,7 +1,7 @@
 module.exports = {
   presets: [
     // Used for Vue applications.
-    '@vue/app',
+    [ '@vue/app', { useBuiltIns: 'entry' } ]
   ],
   plugins: [
     // Allows us to directly include modules that use CommonJS (like phyx.js).