Revert "Update babel-preset-es2015 to version 6.13.0 🚀" (#2469)

Author: flovilmart

package.json

@@ -53,7 +53,7 @@
     "babel-core": "6.11.4",
     "babel-plugin-syntax-flow": "6.13.0",
     "babel-plugin-transform-flow-strip-types": "6.8.0",
-    "babel-preset-es2015": "6.13.0",
+    "babel-preset-es2015": "6.6.0",
     "babel-preset-stage-0": "6.5.0",
     "babel-register": "6.9.0",
     "codecov": "1.0.1",