Fix some issues reported by lintian

Fix some issues reported by lintian

• Trim trailing whitespace. (trailing-whitespace)

• Bump debhelper from old 12 to 13. (package-uses-old-debhelper-compat-version)

• Set upstream metadata fields: Repository-Browse. (upstream-metadata-file-is-missing)

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Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/k4dirstat/f708324c-48b2-4039-a8dd-bd2bb7c646e9.

Debdiff

These changes affect the binary packages:

[The following lists of changes regard files as different if they have different names, permissions or owners.]

Files in second set of .debs but not in first

-rw-r--r--  root/root   /usr/lib/debug/.build-id/79/0e47c241a8a64c544984f38110f51f49c492e8.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/68/390e787a3d2ba8b7b2dea88598c70b6e88aacd.debug

No differences were encountered between the control files of package **k4dirstat**

Control files of package k4dirstat-dbgsym: lines which differ (wdiff format)

• Build-Ids: 68390e787a3d2ba8b7b2dea88598c70b6e88aacd 790e47c241a8a64c544984f38110f51f49c492e8

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