Steel-types are immune to the poison status in Gen 3+, so wrap it into the
"fail when the opposing Pokemon is immune to the status it sets" and set
up the poison-inflicting status test to check Generation 2.
Spin off Thunder Wave to its own test, and also create a test for Glare to
check its Generation 3 behavior as well.
- Streams are merged to make sure that all errors and warnings are reported.
- Adds dev dependencies: `merge-stream` and `lazypipe`.
- Tracks a fork of `gulp-jshint` to fix https://github.com/spalger/gulp-jshint/issues/88
