add: core-js依赖

Author: gorkys

package.json

@@ -34,6 +34,7 @@
     "babel-plugin-istanbul": "^5.2.0",
     "babel-preset-vue": "^2.0.2",
     "chai": "^4.1.2",
+    "core-js": "^2.6.11",
     "cross-env": "^5.2.1",
     "git-directory-deploy": "^1.5.1",
     "karma": "^4.3.0",