fix(@angular/pwa): support ng add with CLI 6.0.x

Fixes angular#11663

Author: clydin

packages/angular/pwa/pwa/index.ts

@@ -136,7 +136,7 @@ function addManifestToAssetsConfig(options: PwaOptions) {
 }
 
 export default function (options: PwaOptions): Rule {
-  return (host: Tree) => {
+  return (host: Tree, context: SchematicContext) => {
     const workspace = getWorkspace(host);
     if (!options.project) {
       throw new SchematicsException('Option "project" is required.');
@@ -166,6 +166,6 @@ export default function (options: PwaOptions): Rule {
       mergeWith(assetsTemplateSource),
       updateIndexFile(options),
       addManifestToAssetsConfig(options),
-    ]);
+    ])(host, context);
   };
 }