[fix] catch template precompile errors

Fixes a race condition with the precompiler where we were not returning
a promise, and thus it was continuing down the compile chain while files
were still being compiled

This also fixes the issue of the roots watch command hard exiting when
an error occured while compiling the jade

fixes #361
Merge pull request #362 from jenius/sjs/fix-precompiler

[fix] catch template precompile errors