Update script-servo

[Mark-Simulacrum]

Fixes #664

[nnethercote]

This should be called script-servo-2, like hyper-2.

[Mark-Simulacrum]

I was debating that, actually - it's now pretty trivial for us to rename old runs, so we could just rename the old one. But that's probably more hassle than it's worth, so I'll go ahead and update this as you suggest.

[Mark-Simulacrum]

It looks like this is likely a regression in build times -- previously I believe we didn't run bindgen on every (commit) of script-servo but now we will. It doesn't look like this is readily changeable either... I'm going to merge this in and deploy to the collector, though, and we'll see how our queue looks like after a few days. If needed we can explore "vendoring" or something.