fix(package): update core-js to version 3.4.6

Closes #149

Author: greenkeeper[bot]

package.json

@@ -22,7 +22,7 @@
     "@angular/platform-browser-dynamic": "^4.1.3",
     "@angular/router": "^4.1.3",
     "angular-in-memory-web-api": "^0.3.2",
-    "core-js": "^2.4.1",
+    "core-js": "^3.4.6",
     "foundation-sites": "^6.3.1",
     "global": "^4.3.2",
     "normalize.css": "^8.0.1",