Upgrade core-js 2.5.7 -> 2.6.0

Author: ehmicky

package-lock.json

@@ -51,7 +51,7 @@
   "dependencies": {
     "@babel/runtime": "^7.2.0",
     "chalk": "^2.4.1",
-    "core-js": "^2.5.7",
+    "core-js": "^2.6.0",
     "jest-validate": "^23.6.0",
     "moize": "^5.4.1",
     "supports-color": "^5.5.0"