lintian: priority should be optional not extra

[themusicgod1]

when building this package lintian does:

Now running lintian golang-github-mattn-go-runewidth_0.0.2+git20170510.3.97311d9-1ubuntu2_amd64.changes ...
W: golang-github-mattn-go-runewidth-dev: priority-extra-is-replaced-by-priority-optional
W: golang-github-mattn-go-runewidth-dev: package-has-long-file-name 81 > 80
Finished running lintian.

this occurs on both bionic and cosmic versions of golang-github-mattn-go-runewidth
( eg both 0.0.2+git20170510.3.97311d9-1ubuntu2 ).

Included patch changes priority to 'optional' which shuts lintian up.

lintian: 2.5.111

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: golang-github-mattn-go-runewidth-dev 0.0.2+git20170510.3.97311d9-1ubuntu2
ProcVersionSignature: Ubuntu 4.18.0-10.11-generic 4.18.12
Uname: Linux 4.18.0-10-generic x86_64
ApportVersion: 2.20.10-0ubuntu13
Architecture: amd64
Date: Sat Nov 10 20:36:58 2018
Dependencies:

PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: golang-github-mattn-go-runewidth
UpgradeStatus: Upgraded to cosmic on 2018-08-07 (95 days ago)

[Graham Inggs (ginggs)]

golang-github-mattn-go-runewidth (0.0.4-1) unstable; urgency=medium

  [ Alexandre Viau ]
  * Point Vcs-* urls to salsa.debian.org.

  [ Anthony Fok ]
  * New upstream version 0.0.4
  * Add filenamemangle option in debian/watch
  * Apply "cme fix dpkg" fixes to debian/control,
    setting Priority to optional, bumping Standards-Version to 4.2.1, etc.
  * Update Maintainer email address to <email address hidden>
  * Use debhelper (>= 11~)

 -- Anthony Fok <email address hidden> Thu, 20 Dec 2018 13:21:03 -0700