changed doc generation code again

appveyor.yml

@@ -78,11 +78,11 @@ before_deploy:
                 { New-Item -ItemType directory -Path origin_site/tags }
             }
             
-            function Do-DocFX($params)
+            function Do-DocFX([string]$params)
             {
                 Add-Content link_branch.json "{`"_gitContribute`":{`"sourceBranch`":`"$env:APPVEYOR_REPO_COMMIT`",`"apiSpecFolder`":`"docs/override`"}}"
                 & docfx metadata
-                Invoke-Expression "& docfx build --globalMetadataFiles link_branch.json $params"
+                & "docfx build --globalMetadataFiles link_branch.json $params"
                 if ($lastexitcode -ne 0){
                   throw [System.Exception] "docfx build failed with exit code $lastexitcode."
                 }
@@ -108,7 +108,7 @@ before_deploy:
             }
             elseif (-Not $env:APPVEYOR_PULL_REQUEST_TITLE)
             { # Generate docs
-                Do-DocFX
+                Do-DocFX ""
                 
                 Git-Do