Fix some issues reported by lintian

Fix some issues reported by lintian

• Add missing debian/rules targets build-indep, build-arch. (debian-rules-missing-recommended-target)
• Update standards version to 4.6.1, no changes needed. (out-of-date-standards-version)
• Update lintian override info format in d/source/lintian-overrides on line 3. (mismatched-override)
• Update standards version to 4.6.2, no changes needed. (out-of-date-standards-version)

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/b0/fad827869011f639c5a157a9bbfbd7f543e8d4.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/ca/216206b5756a3be324076347a1ef1bf259aaea.debug

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

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

• Build-Ids: ca216206b5756a3be324076347a1ef1bf259aaea b0fad827869011f639c5a157a9bbfbd7f543e8d4

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Build and test logs for this branch can be found at https://janitor.debian.net/run/9cb8dfa5-9c45-49d8-9909-c0ff1ad96975.