Travis builds are failing with fatal listen error

My Travis tests for a Rails app have been working fine, but have suddenly started failing about one time in three with:

$ bundle exec rails test
FATAL: Listen error: unable to monitor directories for changes.
Visit 
https://github.com/guard/listen/wiki/Increasing-the-amount-of-inotify-watchers 
for info on how to fix this.

Looking at that suggested URL, it proposes ways to increase the number of inotify-watchers, but requires the use of sudo to change the limit. That's fine on my dev machine (though I'm actually not experiencing the error on my machine), but I don't know if that's possible (or advisable) in the Travis environment.

I looked at the Travis docs to see if there's a config setting for increasing the number of watchers, but I couldn't find anything.

So: what's the best way to deal with this error in a Travis CI test?