Addressing Port submission failures on Travis

[Ken Cunningham]

> On Dec 20, 2017, at 1:04 AM, Mojca Miklavec <mojca at macports.org> wrote:
> 
>> On 20 December 2017 at 09:04, Ken Cunningham wrote:
>> keep the master branch up to date, but leave your PR branch alone until it's merged, then delete the branch.
> 
> Indeed, that's the correct advice. You only ever need one single fork
> of macports-ports, but make sure to always keep the master branch 100%
> clean (in sync with upstream) and then make a new branch for each PR.
> 
> If you PR needs an update, you push all the changes to that branch and
> that will be properly reflected in the PR. You can even force push to
> fix mistakes in the initial commit or after "git rebase master" etc.
> You cannot have a single branch for multiple PRs, but more important:
> if you modify the master branch, you'll run in all kinds of troubles
> when merging/rebasing etc., so just remember the rule of one branch
> per PR.
> 
> Sometimes people close a PR and open a new one just to fix mistakes.
> This is not needed either as one can simply update the branch and the
> PR will properly reflect that.
> 
> Mojca

The only hiccup comes if the PR lingers and some change is made in master that now requires a change in the PR to  resolve a conflict. Frquently this is when I ran into trouble, so perhaps Mojca might describe the best approach to updating the PR for this issue (eg the qt4-mac PR that needs this done right now ).