Remove yarn dependency duplication.

[texodus]

Cleans up duplicate yarn.lock entries by tightening some dependency ranges, as discussed in #906

[sebinsua]

Btw there is a useful package to get visibility of this kind of thing and which can automate fixing it. Maybe you've used it before - just mentioning it because it's a lot easier than needing to do this manually.

[texodus]

Thanks @sebinsua ! The key thing missing here was a node.js version constraint to our dev dependencies, as emscripten and our Docker runtimes are somewhat inflexibly tied to 8.x