removed the branches endpoint

we already have branch info accessible via the repos endpoints, having this at the root level doesn't make sense.
Update gemspec
Add specs for RemoveLog service

Status code is debatable; I opted for 422 when the job is still
running, and for 500 if unexpected error happened
Update gems
Bring 'logs' table up to date

So that removed_* columns are added
Retry bundle install
Duplicate travis_retry()
Use bash function, not PowerShell
Add RemoveLog service endpoint to jobs/:id/log

This replaces https://github.com/travis-ci/travis-api/pull/107.
Standardize error handling for RemoveLog service endpoints

Return status 409 for errors
Clean up error handling for RemoveLog

With the error message change in travis-core, we can handle
2 exceptions in one rescue clause
DRY up log patching logic

Move the shared logic into a Helpers method so that there is no
code duplication
Tweak RemoveLog helper

Leave responding up to the endpoint
Remove unnecessary parameter from the helper's parameter
Update README [skip ci]

API now requires that `logs` table should be set up properly
Remove `PATCH logs/:job_id` endpoint

To eradicate unnecessary inconsistency.

Spec to test the existing `GET logs/:id` remains.
Merge pull request #94 from travis-ci/jk_remove_branches_endpoint

Remove the branches endpoint
regenerate gemspec
add endpoint for linting
Merge pull request #123 from travis-ci/rkh-lint

add endpoint for .travis.yml linting
Revert "removed the branches endpoint"

This reverts commit f7450cdb6b195e5220b6568f2fbf07db88171dd0.