Fix v2.3.0 build errors

[cpick]

The v2.3.0 relesase has been merged into the debian branch in commit 9b97f6f (see #1), but the code does not build as previous versions had.

Currently, doing a dpkg-buildpackage -us -uc failes with:

dpkg-buildpackage: source package hub
dpkg-buildpackage: source version 2.3.0-0ubuntu0ppa1
dpkg-buildpackage: source distribution xenial
dpkg-buildpackage: source changed by Chris Pick <chris@chrispick.com>
dpkg-buildpackage: host architecture amd64
 dpkg-source --before-build src
 fakeroot debian/rules clean
dh clean --buildsystem=golang --with=golang
   dh_testdir -O--buildsystem=golang
   dh_auto_clean -O--buildsystem=golang
   dh_clean -O--buildsystem=golang
 dpkg-source -b src
dpkg-source: warning: no source format specified in debian/source/format, see dpkg-source(1)
dpkg-source: info: using source format '1.0'
dpkg-source: warning: Version number suggests Ubuntu changes, but Maintainer: does not have Ubuntu address
dpkg-source: warning: Version number suggests Ubuntu changes, but there is no XSBC-Original-Maintainer field
dpkg-source: warning: source directory 'src' is not <sourcepackage>-<upstreamversion> 'hub-2.3.0'
dpkg-source: info: building hub in hub_2.3.0-0ubuntu0ppa1.tar.gz
dpkg-source: info: building hub in hub_2.3.0-0ubuntu0ppa1.dsc
 debian/rules build
dh build --buildsystem=golang --with=golang
   dh_testdir -O--buildsystem=golang
   dh_update_autotools_config -O--buildsystem=golang
   dh_auto_configure -O--buildsystem=golang
   dh_auto_build -O--buildsystem=golang
can't load package: package github.com/github/hub: no buildable Go source files in /home/ubuntu/src/obj-x86_64-linux-gnu/src/github.com/github/hub
	go install -v
can't load package: package .: no buildable Go source files in /home/ubuntu/src/obj-x86_64-linux-gnu
dh_auto_build: go install -v returned exit code 1
debian/rules:9: recipe for target 'build' failed
make: *** [build] Error 1
dpkg-buildpackage: error: debian/rules build gave error exit status 2