Update config to enable docfx v3

Author: VSC-Service-Account

.openpublishing.publish.config.json

@@ -7,7 +7,9 @@
       "build_output_subfolder": "vcppdocs",
       "locale": "en-us",
       "monikers": [],
-      "moniker_ranges": [">= vs-2015"],
+      "moniker_ranges": [
+        ">= vs-2015"
+      ],
       "open_to_public_contributors": true,
       "type_mapping": {
         "Conceptual": "Content",
@@ -56,5 +58,8 @@
     }
   },
   "need_generate_pdf": false,
-  "need_generate_intellisense": false
-}
+  "need_generate_intellisense": false,
+  "docs_build_engine": {
+    "name": "docfx_v3"
+  }
+}