MCOP-181 Add travis build icon to verify travis is working
Update the test matrix for supported rubies

Drop 1.8.7 from the test matrix as we don't support it. Add 2.0.0.
fixup stubbing on Travis/Linux nodes

FileUtils.remove_entry_secure uses File.open on the Linux nodes that travis-ci
runs your tests on, so we need to unstub that too.
Merge pull request #1 from richardc/verify_travis

MCOP-181 Add travis build icon to verify travis is working