Fix "The 'licenseUrl' element will be deprecated" error (#666)

When generating the package, the NuGet task emits this warning:

> The 'licenseUrl' element will be deprecated. Consider using the 'license' element instead.

Since `TreatWarningsAsErrors` is set to true in Directory.Build.props it becomes an error.

So we simply ignore this warning since we can't use 'license' instead of 'licenseUrl' yet.

See also NuGet/Home#7509 and NuGet/Announcements#32

Author: 0xced

src/Microsoft.Azure.ServiceBus/Microsoft.Azure.ServiceBus.csproj

@@ -23,7 +23,7 @@
     <GenerateAssemblyCompanyAttribute>false</GenerateAssemblyCompanyAttribute>
     <GenerateAssemblyProductAttribute>false</GenerateAssemblyProductAttribute>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
-    <NoWarn>CS1591;CS1573</NoWarn>
+    <NoWarn>CS1591;CS1573;NU5125</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>