Bugfix to resolve babel in Opera.

package.json

@@ -20,6 +20,7 @@
     "babel-core": "^6.26.0",
     "babel-loader": "^7.1.2",
     "babel-preset-es2015": "^6.24.1",
+    "babel-preset-stage-2": "^6.24.1",
     "compression-webpack-plugin": "^1.0.1",
     "file-loader": "^1.1.5",
     "mithril": "^1.1.5",