prepare WCF Client 6.2 GA release (#5346)

Author: HongGit

eng/Versions.props

@@ -8,7 +8,7 @@
     <WcfAssemblyVersion>6.2.0.0</WcfAssemblyVersion>
     <!-- To produce shipping versions in non-official builds, instead of default fixed dummy version number (42.42.42.42). -->
     <DotNetUseShippingVersions>true</DotNetUseShippingVersions>
-    <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
+    <PreReleaseVersionLabel>rtm</PreReleaseVersionLabel>
     <PreReleaseVersionIteration>
     </PreReleaseVersionIteration>
     <!-- Opt-in repo features -->