[Checkins] [zopefoundation/z3c.schema] 0e6da7: Install the test extra.

[GitHub]

  Branch: refs/heads/fix4
  Home:   https://github.com/zopefoundation/z3c.schema
  Commit: 0e6da7bb3f09a93d82370fb3824bd065c907980e
      https://github.com/zopefoundation/z3c.schema/commit/0e6da7bb3f09a93d82370fb3824bd065c907980e
  Author: Jason Madden <jamadden at gmail.com>
  Date:   2016-09-12 (Mon, 12 Sep 2016)

  Changed paths:
    M .travis.yml

  Log Message:
  -----------
  Install the test extra.

This cleans up the test output by having all deps installed before it
starts.

It's also necessary for `cache: pip` to work well. But experiments show
that (until we have more dependencies) our runtime is dominated by
Travis setup, not by anything we do, so it's break-even at best. See a
fully cached example here: https://travis-ci.org/zopefoundation/z3c.schema/builds/159302167