downgrade core-js

package.json

@@ -41,7 +41,7 @@
     "chokidar": "^0.12.6",
     "commander": "^2.6.0",
     "convert-source-map": "^0.5.0",
-    "core-js": "^0.7.0",
+    "core-js": "^0.6.0",
     "debug": "^2.1.1",
     "detect-indent": "^3.0.0",
     "estraverse": "^1.9.1",
@@ -64,6 +64,7 @@
     "slash": "^1.0.0",
     "source-map": "^0.4.0",
     "source-map-support": "^0.2.9",
+    "tmp": "0.0.25",
     "to-fast-properties": "^1.0.0",
     "trim-right": "^1.0.0"
   },