Update WPF master branding to RC1 (release candidate 1) (#3253)

eng/Versions.props

@@ -2,8 +2,8 @@
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
     <VersionPrefix>5.0.0</VersionPrefix>
-    <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
-    <PreReleaseVersionIteration>8</PreReleaseVersionIteration>
+    <PreReleaseVersionLabel>rc</PreReleaseVersionLabel>
+    <PreReleaseVersionIteration>1</PreReleaseVersionIteration>
     <SystemIOPackagingVersion>5.0.0-preview.8.20363.2</SystemIOPackagingVersion>
     <SystemResourcesExtensionsVersion>5.0.0-preview.8.20363.2</SystemResourcesExtensionsVersion>
   </PropertyGroup>