Bump preview version to 7.1.0

Author: Shane32

Directory.Build.props

@@ -1,7 +1,7 @@
 <Project>
 
   <PropertyGroup>
-    <VersionPrefix>6.1.0-preview</VersionPrefix>
+    <VersionPrefix>7.1.0-preview</VersionPrefix>
     <LangVersion>12.0</LangVersion>
     <Copyright>Shane Krueger</Copyright>
     <Authors>Shane Krueger</Authors>