(#5191) - disable npm progress bar in Travis

[nolanlawson]

Apparently this still has a ~5% perf impact in npm@3 (npm/npm#11283 (comment)). See also jashkenas/backbone#3938 for some others who are doing this. If this doesn't speed up our npm installs, we can remove it, but currently npm install is taking ~160 seconds in Travis, so getting that down seems like a worthy endeavor.

[nolanlawson]

Compared a couple runs: before and after. Taking the median of three Node runs in each, and only measuring the npm install, we get

before: 190.98, 175.84, 157.07 -> 175.84
after: 164.14, 157.5, 162.31 -> 162.31
improvement: 7.69%

So this does indeed seem to make our npm installs faster, and probably other npm tasks too. Looking at the overall build times between those two builds, it seems to shave off as much as 30 seconds (some builds are slightly slower though - probably just normal variation).

Given that this is a one-line code change, it's probably worth it.

[daleharvey]

Yeh this seems good, cheers

[samccone]

seems like I should do another look now at the perf hit.... for npm.

since time npm i is very variable