Disable parallel bundle installs causing failures on rbx

https://github.com/travis-ci/travis-ci/issues/2821
https://github.com/mvz/rubocop/commit/345a90957c2f16861356d887e23733a43f85ca56
Merge pull request #12 from brandondunne/disable_concurrent_bundle_install

Disable parallel bundle installs causing failures on rbx
Latest version of rest-client.

ssl_version option was added to manageiq vendor/gems/rest-client in 2012
The vendored gem was moved into manageiq/rest-client repo.

#ManageIQ/rest-client@0354d26

The patch we applied: L2G/rest-client-fork#3 was basically 123
rest-client/rest-client#123 was added to rest-client 1.6.7 but later removed
final: rest-client/rest-client#140 (which has since been tweaked)