Update appveyor.yml

it cannot cache if size larger than 1gb 
so delete unnecessary files

appveyor.yml

@@ -39,6 +39,8 @@ install:
 
     $dataPath = $steamData.Replace("/", "\")
     
+    Remove-Item -LiteralPath $dataPath\Content -Force -Recurse
+
     cmd /S /C mklink /J .\GameBinaries $dataPath\DedicatedServer64
 cache:
 - c:\steam\dedi\