fix(@schematics/angular): set proper severity of the tslint deprecation rule

Author: mgechev

packages/schematics/angular/workspace/files/tslint.json.template

@@ -7,7 +7,7 @@
     "array-type": false,
     "arrow-parens": false,
     "deprecation": {
-      "severity": "warn"
+      "severity": "warning"
     },
     "import-blacklist": [
       true,
@@ -77,4 +77,4 @@
     "use-lifecycle-interface": true,
     "use-pipe-transform-interface": true
   }
-}
+}