Fixed Github download URL

Fixed github download URL (was a 400).

This makes #63 obsolete. The difference between #63 and this PR is the filename of the downloaded zip (`SublimeTODO-1.1.3.zip` for this PR vs `robcowie-SublimeTODO-1.1.3-0-gdd699a4.zip` for #63). Don't know if that will actually make a difference.