Doctr not pushing index.html for pull request branches

[asmeurer]

See https://github.com/drdoctr/doctr/tree/gh-pages/docs-retry

[asmeurer]

Looks like it was broken by #215 somehow b245bd4

[asmeurer]

It's because I added docs/_build/html/index.html to gh-pages for testing, but the test didn't actually pass. If you have an untracked file in one branch that is tracked in another, git will just replace it when you check out the other branch without any warnings.

[asmeurer]

git stash has an --include-untracked flag. Should do what we want.