fixed git push fail when GITLAB_PORT is not 80

I map the 80 port to Docker host's 8888 and access gitlab via host ip ,use  params:
`-e "GITLAB_HOST={host ip}" -e "GITLAB_PORT=8888" `
when use `git push`, I got some error:
```
/usr/lib/ruby/2.0.0/net/http.rb:878:in `initialize': Connection refused - connect(2) (Errno::ECONNREFUSED)
	from /usr/lib/ruby/2.0.0/net/http.rb:878:in `open'
	from /usr/lib/ruby/2.0.0/net/http.rb:878:in `block in connect'
	from /usr/lib/ruby/2.0.0/timeout.rb:52:in `timeout'
	from /usr/lib/ruby/2.0.0/net/http.rb:877:in `connect'
	from /usr/lib/ruby/2.0.0/net/http.rb:862:in `do_start'
	from /usr/lib/ruby/2.0.0/net/http.rb:851:in `start'
	from /home/git/gitlab-shell/lib/gitlab_net.rb:75:in `get'
	from /home/git/gitlab-shell/lib/gitlab_net.rb:30:in `allowed?'
	from /home/git/gitlab-shell/lib/gitlab_shell.rb:59:in `validate_access'
	from /home/git/gitlab-shell/lib/gitlab_shell.rb:23:in `exec'
	from /home/git/gitlab-shell/bin/gitlab-shell:16:in `<main>'
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
```

Found `gitlab_url` in  `/home/git/gitlab-shell/config.yml` is `{GITLAB_HOST}` but not `{GITLAB_HOST}:{GITLAB_PORT}`