Yarn support

[duboff]

Hi, we love Doppins but since switching to https://github.com/yarnpkg/yarn it has become a bit of a pain since Doppins does not update the lockfile. A solution would be to run yarn command for every PR.

I wanted to open a PR myself but couldn't so far figure out where this code should go.

[ekmartin]

Sorry for the late reply. This is definitely something we want to support however, and we've discussed it previously. Optimally we'd only want a PR to include changes to yarn.lock related to the dependency it tries to upgrade. I.e. if a PR upgrades express it shouldn't update the version for transient dependencies not created by express.

I think this might be achieved by using yarn upgrade [email protected], but have to verify that it doesn't make other changes to the lock file as well. The problem with this however is that it requires yarn to actually install the dependencies, something we'd rather avoid if possible. I'm not sure if it's possible to generate yarn lock-files without actually installing dependencies though - will have to investigate.