Change PreReleaseVersionLabel from 'preview1' to 'rtw' for 2.3.0 (#662)

Author: twsouthwick

eng/Versions.props

@@ -8,7 +8,7 @@
     <MajorVersion>2</MajorVersion>
     <MinorVersion>3</MinorVersion>
     <PatchVersion>0</PatchVersion>
-    <PreReleaseVersionLabel>preview1</PreReleaseVersionLabel>
+    <PreReleaseVersionLabel>rtw</PreReleaseVersionLabel>
     <DotNetFinalVersionKind Condition="'$(PreReleaseVersionLabel)' == 'rtw'">release</DotNetFinalVersionKind>
   </PropertyGroup>
   <PropertyGroup>