Update watch file format version to 4.

Changes-By: lintian-brush
Fixes: lintian: older-debian-watch-file-standard
See-also: https://lintian.debian.org/tags/older-debian-watch-file-standard.html

debian/changelog

@@ -1,3 +1,9 @@
+dulwich (0.20.15-2) UNRELEASED; urgency=medium
+
+  * Update watch file format version to 4.
+
+ -- Jelmer Vernooij <jelmer@debian.org>  Wed, 03 Mar 2021 17:14:44 -0000
+
 dulwich (0.20.15-1) unstable; urgency=medium
 
   [ Debian Janitor ]

debian/watch

@@ -1,3 +1,2 @@
-version=3
-opts="pgpsigurlmangle=s/$/.asc/" \
-	 https://pypi.debian.net/dulwich/dulwich-(.*).tar.gz
+version=4
+opts=pgpsigurlmangle=s/$/.asc/ https://pypi.debian.net/dulwich dulwich-(.*).tar.gz