Adds babel-core which is needed for ava.

Author: skellock

package.json

@@ -45,6 +45,7 @@
   "devDependencies": {
     "ava": "^0.14.0",
     "babel-cli": "^6.7.5",
+    "babel-core": "^6.7.7",
     "babel-plugin-transform-object-rest-spread": "^6.6.5",
     "babel-preset-es2015": "^6.6.0",
     "babel-preset-stage-0": "^6.5.0",