Enable msbuild in action

Author: dotMorten

.github/workflows/ghpages.yml

@@ -14,6 +14,9 @@ jobs:
 
     - name: Clone Repo
       uses: actions/checkout@v1
+    
+    - name: Setup Visual Studio Command Prompt
+      uses: microsoft/[email protected]
 
     - name: Download DocFX
       run: |