Accept travis.yml for CI

Description

Many times I have projects that are based on GitHub, because I need to submit PRs there, however, I like to keep them mirrored to gitlab.com, to associate my contributions with my profile. I'd also like to be able to have CI on mirrored projects, with travis configuration. I know this is a lot of work, but it would be amazingly helpful to also have the CI jobs running on GitLab, making it "fully" mirrored.

Links / references

The travis configuration syntax
Travis env variables, that would likely need to also be cloned.