Update prerelease for public preview.

Author: vidai-msft

src/DnsResolver/DnsResolver/Az.DnsResolver.psd1

@@ -144,7 +144,7 @@ PrivateData = @{
         ReleaseNotes = '* Upgraded nuget package to signed package.'
 
         # Prerelease string of this module
-        # Prerelease = ''
+        Prerelease = 'preview'
 
         # Flag to indicate whether the module requires explicit user acceptance for install/update/save
         # RequireLicenseAcceptance = $false