Attempt to fix powershell doc gen stuff again

Author: natemcmaster

docs/generate.ps1

@@ -17,7 +17,7 @@ try {
     mkdir -p $buildRoot -ErrorAction Ignore | Out-Null
 
     if (-not (git worktree list --porcelain | Select-String 'gh-pages')) {
-        exec git fetch --quiet origin gh-pages:gh-pages
+        exec git fetch --quiet -u origin gh-pages:gh-pages
         exec git worktree add $targetDir gh-pages
     }
 

src/common.psm1

@@ -1,7 +1,7 @@
 function exec([string]$_cmd) {
     write-host -ForegroundColor DarkGray ">>> $_cmd $args"
     $ErrorActionPreference = 'Continue'
-    & $_cmd @args 2>&1
+    & $_cmd @args
     $ErrorActionPreference = 'Stop'
     if ($LASTEXITCODE -ne 0) {
         write-error "Failed with exit code $LASTEXITCODE"