Use secure copyright file specification URI.

Fixes lintian: insecure-copyright-format-uri
See https://lintian.debian.org/tags/insecure-copyright-format-uri.html for more details.

debian/changelog

@@ -1,3 +1,9 @@
+dulwich (0.19.9-2) UNRELEASED; urgency=medium
+
+  * Use secure copyright file specification URI.
+
+ -- Jelmer Vernooij <jelmer@debian.org>  Mon, 19 Nov 2018 19:53:42 +0000
+
 dulwich (0.19.9-1) unstable; urgency=medium
 
   * New upstream release.

debian/copyright

@@ -1,4 +1,4 @@
-Format: http://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
 Upstream-Name: dulwich
 Upstream-Contact: Jelmer Vernooij <jelmer@jelmer.uk>
 Source: https://www.dulwich.io/