Ensure offline repository is added to sbt-rc.

This should fix offline mode.  However, I couldn't find where/how
this was working without this fix.  This was created specifically
for offline  mode to work.   Not sure how we limped along
without it.
Merge pull request #118 from typesafehub/wip-jsuereth-fix-offline-mode

Ensure offline repository is added to sbt-rc.