chore(package): update @angular/language-service to version 6.0.1

Closes #28

Author: greenkeeper[bot]

package.json

@@ -50,7 +50,7 @@
   "devDependencies": {
     "@angular/cli": "1.7.1",
     "@angular/compiler-cli": "^5.2.6",
-    "@angular/language-service": "^5.2.6",
+    "@angular/language-service": "^6.0.1",
     "@types/body-parser": "^1.16.8",
     "@types/chai": "^4.1.2",
     "@types/chai-http": "^3.0.4",