Refering to underscore.js instead of underscore-min.js in unit.html.

There are two reasons for this change:
  1) It fixes failures in downstream repositories due to the lack of
     underscore-min.js in the npm package for underscore.
  2) You actually want to use underscore.js to enable easier debugging
     of your test failures (contrived, but true).
Merge pull request #148 from dotskapes/qunit_underscore_fix

Refering to underscore.js instead of underscore-min.js in unit.html.