fixes #16
fixes #16

Because of the way we set the `sbt.boot.directory`
it was trying to store the .sbt directory in /
if the `$WORKSPACE` environment variable was not
set. Now it will use the user's home directory
if `$WORKSPACE` is not set.

gorcz/atlas,rspieldenner/atlas,gorcz/atlas,Netflix/atlas,rspieldenner/atlas,Netflix/atlas,jasimmk/atlas,jasimmk/atlas,brharrington/atlas,rspieldenner/atlas,rspieldenner/atlas,copperlight/atlas,copperlight/atlas,jasimmk/atlas,brharrington/atlas,gorcz/atlas,gorcz/atlas,jasimmk/atlas,brharrington/atlas,Netflix/atlas,copperlight/atlas