Fix upstream repository URLs.

debian/upstream/metadata

@@ -1,6 +1,6 @@
 Name: dulwich
-Repository: https://www.dulwich.io/code/
-Repository-Browse: https://www.dulwich.io/code/
+Repository: https://www.dulwich.io/code/dulwich/
+Repository-Browse: https://www.dulwich.io/code/dulwich/
 Bug-Database: https://github.com/dulwich/dulwich/issues
 Bug-Submit: https://github.com/dulwich/dulwich/issues/new
 Contact: https://groups.google.com/forum/#!forum/dulwich-discuss