Update ICSharpCode.Decompiler.nuspec.template

Fix per nuget push error on build " warn : No destination repository detected. Ensure the source project has a 'RepositoryUrl' property defined. If you're using a nuspec file, ensure that it has a repository element with the required 'type' and 'url' attributes." See also https://docs.microsoft.com/en-us/nuget/reference/nuspec#repository

ICSharpCode.Decompiler/ICSharpCode.Decompiler.nuspec.template

@@ -8,6 +8,7 @@
 		<owners>Daniel Grunwald, SharpDevelop</owners>
 		<license type="expression">MIT</license>
 		<projectUrl>https://github.com/icsharpcode/ILSpy/</projectUrl>
+		<repository type="git" url="https://github.com/icsharpcode/ILSpy.git" />
 		<icon>images\DecompilerNuGetPackageIcon.png</icon>
 		<requireLicenseAcceptance>false</requireLicenseAcceptance>
 		<description>ICSharpCode.Decompiler is the decompiler engine used in ILSpy.</description>
@@ -27,4 +28,4 @@
 		<file src="bin\$Configuration$\netstandard2.0\ICSharpCode.Decompiler.pdb" target="lib\netstandard2.0" />
 		<file src="bin\$Configuration$\netstandard2.0\ICSharpCode.Decompiler.xml" target="lib\netstandard2.0" />
 	</files>
-</package>
+</package>