Issue when deploying multiple times for same repo

[alexdiliberto]

Reproduction App: https://github.com/alexdiliberto/deploy-dummy-app/commits/gh-pages

1. Create a new app with some dummy code
2. Setup new gh-pages branch
3. Do first deploy using ember deploy production. Looks good.
4. Now make some small change to the code
5. Deploy again using ember deploy production
6. Issue: Notice that my change didn't actually get deployed to https://alexdiliberto.com/deploy-dummy-app/. Also note theres a error when trying to switch to the gh-pages branch

$ git checkout gh-pages
fatal: 'gh-pages' is already checked out at '/private/tmp/deploy'

EDIT: Ok looks like the changes do propagate but it just takes time...I checked again about 15 minutes later (didn't check but probably just a small caching issue). But the gh-pages branch error still persists and you can't switch to that branch

[knownasilya]

I get another error, which is resolved by removing /private/tmp/deploy

 △ ~/sandbox/ember-template-input ember deploy production             ⇡ master :: 0m :: ⬢
cleaning up...
Deploying [🚀 ] 100% [plugin: git -> upload]
There is no tracking information for the current branch.
Please specify which branch you want to merge with.
See git-pull(1) for details.

    git pull <remote> <branch>

If you wish to set tracking information for this branch you can do so with:

    git branch --set-upstream-to=origin/<branch> gh-pages

Error: git pull exited with nonzero status
Error: git pull exited with nonzero status
    at ChildProcess.<anonymous> (/Users/iradchenko/sandbox/ember-template-input/node_modules/ember-cli-deploy-git/lib/run.js:19:19)
    at emitTwo (events.js:106:13)
    at ChildProcess.emit (events.js:191:7)
    at maybeClose (internal/child_process.js:877:16)
Pipeline aborted