Test to fix issue #892 with chrome version change from stable to beta

[suhailnaw]

Summary

Trying to determine what causes 3 of 21 builds to fail, per Issue #892. I already compared the previous working build's gem versions to the broken build and did not find any differences.

The new version of Chrome (from version 64.0.3282.167-1 to 66.0.3359.139-1) might have affected the build, so I want to try to change the Chrome version. It's installed in the travis.yml file, but you're only allowed to specify stable or beta as the version, not a number version of chrome.

I'm creating this pull request because I want to test this change within a Travis build.

[BookOfGreg]

In order to try help diagnosis, I just asked travis to re-run previously passing build 1417.4

https://travis-ci.org/reactjs/react-rails/builds/338407498
The re-run of a previously passing build failed, so the reason has to be something that is not locked changing whether that's chrome or gem locks, or something as-yet unpredicted.