Fix headless browser tests

[enlight]

We had to disable the headless browser tests since they seemed to blow up on Travis CI for some reason. Need to figure out why they're blowing up and re-enable them.

[eduardonunesp]

@enlight what exactly are those headless browser test on loom-js, could you please give me a direction so I can check it

[enlight]

It's these ones that are currently commented out

loom-js/e2e_tests.sh

Line 81 in 877edfc

#yarn test:browser

It's supposed to just webpack everything and run the tests in a headless Electron instance.