fix(package): update core-js to version 3.2.1

Closes #36

Author: greenkeeper[bot]

package.json

@@ -24,7 +24,7 @@
     "@angular/router": "^7.1.4",
     "@ng-bootstrap/ng-bootstrap": "^4.1.1",
     "@ngx-progressbar/core": "^5.3.2",
-    "core-js": "^2.6.1",
+    "core-js": "^3.2.1",
     "rxjs": "^6.3.3",
     "rxjs-tslint": "^0.1.6",
     "socket.io": "^2.2.0",