Upgrade raven.js (Sentry client) to 3.8.1 (#801)
Upgrade raven.js (Sentry client) to 3.8.1 (#801)

We were previously on the 2.x series. I tested this by triggering an error locally in production mode which was successfully logged to Sentry.
travis-ci/travis-web,fotinakis/travis-web,fotinakis/travis-web,travis-ci/travis-web,fotinakis/travis-web,travis-ci/travis-web,fotinakis/travis-web,travis-ci/travis-web