chore(package): update @angular/core to version 5.2.1

Closes #14

Author: greenkeeper[bot]

package.json

@@ -63,7 +63,7 @@
     "@angular/common": "^4.0.0",
     "@angular/compiler": "^4.0.0",
     "@angular/compiler-cli": "^4.0.0",
-    "@angular/core": "^4.0.0",
+    "@angular/core": "^5.2.1",
     "@angular/forms": "^4.0.0",
     "@angular/platform-browser": "^4.0.0",
     "@angular/platform-browser-dynamic": "^4.0.0",