fix($compile): prevent babel from transpiling non-module scripts in default_theme's assets

Transpiling the assets in the default theme was causing `this` to be transpiled to `undefined`. The
Babel config now ignores those files.

888

Author: Jean-Luc Martin

.babelrc

@@ -1,4 +1,7 @@
 {
   "presets": ["es2015", "stage-0", "flow"],
-  "plugins": ["syntax-async-functions"]
+  "plugins": ["syntax-async-functions"],
+  "ignore": [
+      "**/default_theme/assets/*"
+  ]
 }