Temporarily switching to sqlisrv 5.5.0preview on AppVeyor

See microsoft/msphpsql#955

.appveyor.yml

@@ -68,8 +68,7 @@ install:
           Add-Content php.ini "`n extension=php_curl.dll"
           Add-Content php.ini "`n curl.cainfo=C:\tools\cacert\bundle.pem"
 
-          # Get and install the latest stable sqlsrv DLL's
-          $DLLVersion = (Invoke-WebRequest "https://pecl.php.net/rest/r/sqlsrv/stable.txt").Content
+          $DLLVersion = "5.5.0preview"
           cd c:\tools\php\ext
           $source = "https://windows.php.net/downloads/pecl/releases/sqlsrv/$($DLLVersion)/php_sqlsrv-$($DLLVersion)-$($env:php)-nts-vc15-x64.zip"
           $destination = "c:\tools\php\ext\php_sqlsrv-$($DLLVersion)-$($env:php)-nts-vc15-x64.zip"
@@ -79,7 +78,7 @@ install:
           $destination = "c:\tools\php\ext\php_pdo_sqlsrv-$($DLLVersion)-$($env:php)-nts-vc15-x64.zip"
           Invoke-WebRequest $source -OutFile $destination
           7z x -y php_pdo_sqlsrv-$($DLLVersion)-$($env:php)-nts-vc15-x64.zip > $null
-          $DLLVersion = "2.6.0"
+          $DLLVersion = (Invoke-WebRequest "https://pecl.php.net/rest/r/xdebug/stable.txt").Content
           $source = "https://xdebug.org/files/php_xdebug-$($DLLVersion)-$($env:php)-vc15-nts-x86_64.dll"
           $destination = "c:\tools\php\ext\php_xdebug.dll"
           Invoke-WebRequest $source -OutFile $destination