bump Versions.props to 7.0-preview3 (#1872)

Author: deepchoudhery

eng/Versions.props

@@ -15,7 +15,7 @@
   <PropertyGroup>
     <VersionPrefix>7.0.0</VersionPrefix>
     <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
-    <PreReleaseVersionIteration>2</PreReleaseVersionIteration>
+    <PreReleaseVersionIteration>3</PreReleaseVersionIteration>
     <IncludeSourceRevisionInInformationalVersion>False</IncludeSourceRevisionInInformationalVersion>
     <IsServicingBuild Condition="'$(PreReleaseVersionLabel)' == 'servicing'">true</IsServicingBuild>
     <!--