Update babel-preset-es2015 to v6.6.0

Close h5bp#1797

Author: greenkeeperio-bot

package.json

@@ -9,7 +9,7 @@
     "apache-server-configs": "2.14.0",
     "archiver": "^0.21.0",
     "babel-core": "^6.7.2",
-    "babel-preset-es2015": "^6.5.0",
+    "babel-preset-es2015": "^6.6.0",
     "del": "^2.0.2",
     "glob": "^7.0.3",
     "gulp": "^3.9.1",