Enable .travis.yml check and use non-markdown license.

[iphydf]

This change is 

[nurupo]

Undoing the License Markdown conversion you did in all/most of TokTok several weeks ago. I do like plain text licenses better, but why did you change your mind?

Also, you say "Enable .travis.yml check" but I don't see where you have enabled it in the diff. Did you mean to say something along the lines "Format .travis.yml with Travis'es linter/formatter" in the commit message? Unless you have Travis'es linter enabled in //tools/project:build_defs.bzl file, but where is this path even pointing to, it doesn't seem to be in this repo, is that a file from TokTok Stack repo?

[iphydf]

s/several weeks/6 months/.

Main reason: most people don't use markdown license in their repo, so I don't want to enforce that for repos entering the toktok org.
Secondary reason: github recognises the non-markdown version and shows it on the main page of the repo.

[robinlinden]

Reviewed 4 of 4 files at r1.
Reviewable status: 0 of 1 approvals obtained