fix(package): update @angular/core to version 5.1.2

Closes #16

Author: greenkeeper[bot]

package.json

@@ -17,7 +17,7 @@
     "@angular/animations": "^4.0.0",
     "@angular/common": "^4.0.0",
     "@angular/compiler": "^4.0.0",
-    "@angular/core": "^4.0.0",
+    "@angular/core": "^5.1.2",
     "@angular/forms": "^4.0.0",
     "@angular/http": "^4.0.0",
     "@angular/platform-browser": "^4.0.0",