Fix https://docs.microsoft.com/en-us/nuget/reference/nuspec#license (license url being deprecated)

ICSharpCode.Decompiler.Console/ICSharpCode.Decompiler.Console.csproj

@@ -11,7 +11,7 @@
     <Description>Command-line decompiler using the ILSpy decompilation engine</Description>
     <Copyright>Copyright 2011-2018 AlphaSierraPapa</Copyright>
     <PackageProjectUrl>https://github.com/icsharpcode/ILSpy/</PackageProjectUrl>
-    <PackageLicenseUrl>https://opensource.org/licenses/mit-license.php</PackageLicenseUrl>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageIconUrl>https://ilspy.net/images/icon32.png</PackageIconUrl>
     <RepositoryUrl>https://github.com/icsharpcode/ILSpy/</RepositoryUrl>
     <Company />

ICSharpCode.Decompiler/ICSharpCode.Decompiler.nuspec.template

@@ -6,7 +6,7 @@
     <title>ILSpy Decompiler Engine</title>
     <authors>ILSpy Contributors</authors>
     <owners>Daniel Grunwald, SharpDevelop</owners>
-    <licenseUrl>https://opensource.org/licenses/mit-license.php</licenseUrl>
+    <license type="expression">MIT</license>
     <projectUrl>https://github.com/icsharpcode/ILSpy/</projectUrl>
     <iconUrl>https://ilspy.net/images/icon32.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>