Merge pull request #330 from twosigma/travis

Travis
Update README.md
Merge pull request #331 from twosigma/travis

add a bug to test travis
Merge pull request #332 from twosigma/travis

removing bug -- test complete
Update README.md

clarify how to install chromedriver
Update dill version per chromedriver bug.
Merge pull request #335 from twosigma/sjs/update-dill

Update dill version per chromedriver bug.
merge
use the firefox driver