update yargs; closes #3742

[boneskull]

as of v13.2.2, yargs has un-un-supported Node.js v6, so we can now consume it, as well as avoid the deprecation by passing the parser configuration via parserConfiguration() method.

[boneskull]

hmm, this is not good.

[coveralls]

Coverage increased (+0.003%) to 91.69% when pulling d2e28a3 on boneskull/yargs-upgrade into b27bc60 on master.