updated core-js version to latest

Author: 902seanryan

.babelrc

@@ -5,7 +5,7 @@
       "@babel/preset-env",
       {
         "useBuiltIns": "usage",
-        "corejs": 2,
+        "corejs": 3,
         "targets": {
           "android": "5",
           "ios": "10",

dist/SpringRoll-Container-umd.js

@@ -48,7 +48,7 @@
   "dependencies": {
     "@babel/polyfill": "^7.4.3",
     "bellhop-iframe": "^3.2.0",
-    "core-js": "^2.6.5",
+    "core-js": "^3.6.5",
     "whatwg-fetch": "^3.0.0"
   },
   "keywords": [