Update config to enable docfx v3

.openpublishing.publish.config.json

@@ -6,7 +6,9 @@
       "build_output_subfolder": "SignalR_Java",
       "locale": "en-us",
       "monikers": [],
-      "moniker_ranges": ["aspnet-signalr-java"],
+      "moniker_ranges": [
+        "aspnet-signalr-java"
+      ],
       "open_to_public_contributors": true,
       "type_mapping": {
         "Conceptual": "Content",
@@ -66,12 +68,14 @@
       "version": "latest"
     },
     {
-
       "path_to_root": "_dependentPackages/memberpage.plugins",
       "target_framework": "net45",
       "version": "latest",
       "id": "memberpage.plugins",
       "nuget_feed": "https://www.myget.org/F/docfx/api/v2"
     }
-  ]
+  ],
+  "docs_build_engine": {
+    "name": "docfx_v3"
+  }
 }