tools: apply linting to first commit in PRs
First commit:
tools: only use Travis-CI on master branch
Limit Travis-CI to the master branch. One benefit is that it will
simplify the logic for commit message linting.
Second commit:
tools: apply linting to first commit in PRs
Use Travis-CI to check the formatting of the first commit in a pull
request. This will hopefully reduce formatting errors and nits about
them in pull requests.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines