Fixes #10 Latest grunt-contrib-less

Relax version specifier on grunt-contrib-less to accept patch versions
switch to hard version specifier
Merge pull request #10 from jasonkarns/latest_grunt_contrib_less

Projects with no less files shouldn't explode.
Explicitly exit the `lineman run` thread to prevent
the race condition that occurs when we delete the
project directory while the thread is still alive.