use license expression

Author: mattleibow

Util/Xamarin.Kotlin.BindingSupport/nuget/Xamarin.Kotlin.BindingSupport.nuspec

@@ -7,6 +7,7 @@
     <authors>Microsoft</authors>
     <owners>Microsoft</owners>
     <requireLicenseAcceptance>true</requireLicenseAcceptance>
+    <license type="expression">MIT</license>
     <licenseUrl>https://go.microsoft.com/fwlink/?linkid=864999</licenseUrl>
     <projectUrl>https://go.microsoft.com/fwlink/?linkid=864997</projectUrl>
     <description>Various tools to support binding Kotlin libraries for Xamarin.Android</description>