Simplify archetypes' `require` of lineman.

Got some feedback that the old way was a little
intimidating, this way will look a little less
scary, especially as plugins may need to require
the right lineman, and we want to establish this
in the archetype first if they're going to do that.
Merge branch 'master' of github.com:testdouble/lineman
Update testem
0.18.3