Minor improvment to devel/bossa

[jrm]

Summary

Apply suggestion from mat@:

• GH_PROJECT=${PORTNAME:tu} instead of WRKSRC=${WRKDIR}/${PORTNAME:tu}-${GH_TAGNAME}

Update distinfo

Submitted by: mat

Test Plan

portlint -C: looks find
testport: OK (poudriere: 9.3-RELEASE, i386, default options) [1]
testport: OK (poudriere: 9.3-RELEASE, amd64, default options) [2]
testport: OK (poudriere: 10.3-RELEASE, i386, default options) [3]
testport: OK (poudriere: 10.3-RELEASE, amd64, default options) [4]
testport: OK (poudriere: 11.0-RC2, i386, default options) [5]
testport: OK (poudriere: 11.0-RC2, amd64, default options) [6]

[1] http://pkg.awarnach.mathstat.dal.ca/data/9i386-default/2016-09-23_18h24m04s/logs/bossa-1.7.0.a.log
[2] http://pkg.awarnach.mathstat.dal.ca/data/9amd64-default/2016-09-23_18h21m32s/logs/bossa-1.7.0.a.log
[3] http://pkg.awarnach.mathstat.dal.ca/data/10i386-default/2016-09-23_18h21m39s/logs/bossa-1.7.0.a.log
[4] http://pkg.awarnach.mathstat.dal.ca/data/10amd64-default/2016-09-23_18h22m01s/logs/bossa-1.7.0.a.log
[5] http://pkg.awarnach.mathstat.dal.ca/data/11i386-default/2016-09-23_18h22m14s/logs/bossa-1.7.0.a.log
[6] http://pkg.awarnach.mathstat.dal.ca/data/11amd64-default/2016-09-23_18h22m22s/logs/bossa-1.7.0.a.log

[swills]

Approved