Create elm-community/travis-ci

There is an open issue to add Elm support to Travis-CI (https://github.com/travis-ci/travis-build/pull/934). Part of the process of getting Elm support approved is to have a group of at least three people willing to provide support for travis issues related to the language plugin. I think it would be good to have those responsibilities be managed by elm-community.

Myself, @lukewestby, @stoeffel and @rtfeldman will be the initial members of the travis support group.

I'd like to propose the following to bring this into elm-community:

- Create elm-community/travis-ci repo for storing a README, any necessary scripts or tools, and issue tracking related to the travis support
- Add the group to elm-community/Manifesto/maintainers.md
- Add info to elm-community/travis-ci/README for others that might be interested in joining the support team