Upcoming JS fixes and release timeline

[Paul Taylor]

The TypeScript compiler has made breaking changes in recent releases, 
meaning we can't easily upgrade past 3.5 and projects on 3.6+ can't 
compile our types.

I'm working on upgrading our tsc dependency to 3.9. The fixes could 
include a few backwards-incompatible API changes, and might not be done 
in time for the general Arrow 1.0 release.

JS shouldn't block the 1.0 release, so can we exclude JS from 1.0 if the 
fixes aren't ready by then? npm's semantic versioning allows breaking 
changes in any version before 1.0, but not between minor versions after 
1.0. I've heard directly from some of our JS users who'd prefer if we 
made these changes before bumping to 1.0 on npm.

Thanks,

Paul