Updates to Gemfile

This does:

* use micro_migrations from a regular gem (the gist sometimes crapped
  out)
* remove data_migrations (not used anyway)
* update safe_yaml, because 0.9.4 has been yanked meanwhile
* set jruby-openssl to require: false and require it manually in
  hub.rb, because this caused tons of warnings about existing constants
  when running rake
require jruby-openssl in bin/hub
make loading raven conditional
loading raven already is conditional in Travis::Exceptions::Reporter
do not report memory usage if metrics reporting is turned off
do not overwrite GH setup
bump travis-support
bump core and support. Travis::Metrics.setup
bundle update after rebase
declare reporting exchange and builds.linux queue in hub
bundle update after rebase