chore(package): update babel-core to version 6.23.0

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
   "license": "ISC",
   "devDependencies": {
     "babel-cli": "^6.18.0",
-    "babel-core": "^6.18.2",
+    "babel-core": "^6.23.0",
     "babel-istanbul": "^0.12.1",
     "babel-plugin-add-module-exports": "^0.2.1",
     "babel-plugin-transform-es2015-modules-umd": "^6.22.0",