Investigate test timeouts on Circle-CI

[pdehaan]

We seem to have Circle-CI builds fail intermittently on the npm test task. Not sure if it's the browserify or the frontend driver test that's causing a ~10 minute timeout error (I suspect the latter).

But I usually find restarting the build 3-4 times can trick it into passing.

> firefox-send@1.0.2 test:browser /home/ubuntu/send
> browserify test/frontend/frontend.bundle.js -o test/frontend/bundle.js -d && node test/frontend/driver.js


command npm test took more than 10 minutes since last output

[pdehaan]

Pretty sure @dannycoates fixed this by not running the test:browser tests as part of npm test (per /package.json:101).