fix(package): update core-js to version 3.6.1

Closes #141

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
     "bootstrap": "^4.1.3",
     "bootstrap-sass": "^3.4.1",
     "chart.js": "^2.6.0",
-    "core-js": "^2.5.4",
+    "core-js": "^3.6.1",
     "font-awesome": "^4.7.0",
     "jquery": "^3.2.1",
     "ng2-charts": "^2.0.0",