Added travis-ci info to build project in a Docker container.

[DWiechert]

Related articles:

• http://blog.travis-ci.com/2014-12-17-faster-builds-with-container-based-infrastructure/
• http://docs.travis-ci.com/user/workers/container-based-infrastructure/

[DWiechert]

Is it possible to restart this travis ci build now that master is passing to verify this PR doesn't break anything?

[DWiechert]

It seems like those who have write access to the repo can restart the build - http://stackoverflow.com/a/17624403/864369

@vkostyukov, would you mind restarting build 482?

[vkostyukov]

Just restarted it. Thanks!

[DWiechert]

Thanks for restarting it. Looks like it built properly.

[vkostyukov]

Cool! Thanks for the PR!