Fix compile errors on .NET Framework.

Author: teo-tsirpanis

generator/ServiceClientGeneratorLib/ServiceClientGeneratorLib.csproj

@@ -738,6 +738,9 @@
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
 	<PackageReference Include="Microsoft.CSharp" Version="4.4.1" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net45'">
+	<Reference Include="Microsoft.CSharp" />
+  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'net45'">
 	<PackageReference Include="System.CodeDom" Version="6.0.0" />
   </ItemGroup>