Add workaround for rubygems/rubygems#763
Add workaround for rubygems/rubygems#763

This defect in Rubygems 2.2.0 breaks all 1.8.x builds on Travis CI.

Workaround until the fix is deployed is to pin builds to latest 2.1.x
build of Rubygems.

pmahoney/process_shared,pmahoney/process_shared