Fix some issues reported by lintian

* Trim trailing whitespace.

Fixes: lintian: file-contains-trailing-whitespace
See-also: https://lintian.debian.org/tags/file-contains-trailing-whitespace.html

* Bump debhelper from old 9 to 10.

Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html

* Use canonical URL in Vcs-Git.

Fixes: lintian: vcs-field-not-canonical
See-also: https://lintian.debian.org/tags/vcs-field-not-canonical.html