bumping to 1.21.1 for missing build

@travisjeffery it appears that when `1.21.0` was released, `make` didn't get run, so the "browser" version of `mocha.js` did not receive the updates.  I don't think this was intentional (but it might have been; I'm new here), so here's a PR.

This builds is on top of the 1.21.0 tag, which means the ~4 commits since then are not included.  If it's OK to just include that stuff and call it a patch, that's fine, and I'll take care of it.