fix(package): update @angular/forms to version 5.2.1

Closes #17

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
     "@angular/common": "^4.0.0",
     "@angular/compiler": "^4.0.0",
     "@angular/core": "^4.0.0",
-    "@angular/forms": "^4.0.0",
+    "@angular/forms": "^5.2.1",
     "@angular/http": "^4.0.0",
     "@angular/platform-browser": "^4.0.0",
     "@angular/platform-browser-dynamic": "^4.0.0",