Specify Ruby 1.9.3 in Gemfile

* This also, strangely enough, seems to be what is needed to make Herok
  execute `rake assets:precompile` on push.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Switch Gemfile source to with https

Signed-off-by: Alex Coles <alex@alexbcoles.com>