Missing Git tags for 0.19.0 and 0.19.1

[tbroyer]

From the release process docs this should have been done at step 3 when creating GitHub Releases.

Given that 0.19.x are current broken (#418), I don't really care whether those GitHub Releases exist or not (they could point out that they're known to be broken and shouldn't be used, and flagged as "pre-release" so 0.18.1 would still be the version highlighted on the repo main page as the latest release), but IMO there shouldn't be published artifacts (to NPM in this case) without a corresponding Git tag. Feel free to disregard this issue if you disagree.