update prettier config to differentiate node scripts from babel compiled modules

.prettierignore

-/config/
 /node_modules/
 /public/
 /vendor/
-karma.config.js
-webpack.config.js

.prettierrc

 {
   "printWidth": 100,
   "singleQuote": true,
-  "trailingComma": "all"
+  "trailingComma": "es5",
+  "overrides": [
+    {
+      "files": ["app/assets/javascripts/*", "spec/javascripts/*"],
+      "options": {
+        "trailingComma": "all"
+      }
+    }
+  ]
 }