fix(package): update core-js to version 3.4.8

Closes #233

Author: greenkeeper[bot]

package.json

@@ -77,7 +77,7 @@
     "@angular/platform-browser-dynamic": "^4.4.4",
     "@angular/platform-server": "^4.4.4",
     "@angular/router": "^4.4.4",
-    "core-js": "^2.5.1",
+    "core-js": "^3.4.8",
     "hammerjs": "^2.0.8",
     "ie-shim": "^0.1.0",
     "rxjs": "^5.0.1",