feat: add support for Angular v12 (#132)

* update angular-devkit dependencies
* use "$id" instead of deprecated "id" for schema

Author: icepeng

src/deploy/schema.json

@@ -1,5 +1,5 @@
 {
-  "id": "Schema",
+  "$id": "Schema",
   "title": "schema",
   "description": "Deployment of Angular CLI applications to GitHub pages (angular-cli-ghpages)",
   "properties": {

src/ng-add-schema.json

@@ -1,6 +1,6 @@
 {
   "$schema": "http://json-schema.org/schema",
-  "id": "angular-cli-ghpages-ng-add-schematic",
+  "$id": "angular-cli-ghpages-ng-add-schematic",
   "title": "angular-cli-ghpages ng-add schematic",
   "type": "object",
   "properties": {},