chore(package): update @angular/language-service to version 6.0.3

Closes #42

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
   "devDependencies": {
     "@angular/cli": "1.5.1",
     "@angular/compiler-cli": "^5.0.2",
-    "@angular/language-service": "^5.0.0",
+    "@angular/language-service": "^6.0.3",
     "typescript": "~2.6.1"
   }
 }