Since the existing jobs are similar (currently, the `script` keys are
same), move the equal parts to a new shared key to have them in one
place. The new map will receive more content in upcoming commits.
There are a couple ways to declare a build matrix in Travis CI, refer to
https://docs.travis-ci.com/user/build-matrix.
Since upcoming commits will add more ways to run tests, switch the build
matrix from simple OS variation to a more powerful list of jobs.
- "bash-it search term1 [term2]...."
- we are using existing 'bash-it show plugins|aliases|completions'
commands output, to search (with grep) for lines that match the
search terms, and then output the matches.
- wrote a simple unit test that for whatever reason fails on Travis,
so wrapped it in 'if "Darwin"'...
