Fixed az nw sdk version (#12763)

Author: MikhailTryakhov

src/SignalR/SignalR.Test/SignalR.Test.csproj

@@ -11,7 +11,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Azure.Management.Network" Version="20.0.2-preview" />
+    <PackageReference Include="Microsoft.Azure.Management.Network" Version="20.1.0" />
     <PackageReference Include="Microsoft.Azure.Management.PrivateDns" Version="1.0.0" />
     <PackageReference Include="Microsoft.Azure.Management.SignalR" Version="1.1.0" />
   </ItemGroup>