Raise an error when updating the GitHub status fails.

If there's a temporary problem with the GitHub API, we should retry.
Merge pull request #298 from travis-ci/mm-github-status-raise-error

Raise an error when updating the GitHub status fails.
Deal with the case where `language` is an array

Users shouldn't do this, since we only use one language in a build,
but some users have it, and it was a regression to not deal with this.
Merge pull request #309 from travis-ci/ha-bug-lang_array_in_config

Handle the case where `language` is an array
Merge branch 'master' into ha-feature-multi_os_support