format v3.x extension metadata generator as 'versionprefix'

Author: mhoeger

tools/ExtensionsMetadataGenerator/src/ExtensionsMetadataGenerator/ExtensionsMetadataGenerator.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <Import Project="..\..\build\metadatagenerator.props" />
   <PropertyGroup>
-    <Version>1.1.7</Version>
+    <VersionPrefix>1.1.7</VersionPrefix>
     <OutputType>Library</OutputType>
     <TargetFrameworks>netstandard2.0;net46</TargetFrameworks>
     <AssemblyName>Microsoft.Azure.WebJobs.Script.ExtensionsMetadataGenerator</AssemblyName>