not possible to install with yarn due to dependency in git repo

Yarn refuses to install this package as it has a git repo as a dependency due to it not having a hash. Can it be removed and turned into a reference to the npm repository, or it still necessary to keep it?

This is the dep: `git://github.com/mjohnston/scroller`

And this is the error log from `yarn add react-canvas`:

```
yarn add v0.27.5
warning ../../package.json: No license field
warning ../../../../../package.json: No license field
[1/4] Resolving packages...
error Refusing to download the git repo {"hostname":"github.com","protocol":"git:","repository":"git://github.com/mjohnston/scroller.git"} over plain git without a commit hash
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.
```

This is caused by a long-standing issue in yarn: https://github.com/yarnpkg/yarn/issues/2117, and a quick fix might be to specify the commit hash to use.

Start by locating the package manifest entry for the git dependency `git://github.com/mjohnston/scroller`, then check the dependency's available npm package or commit reference. Run `yarn add react-canvas` or the repository's install command to reproduce the Yarn 0.27.5 error; done means installation completes without the plain-git, missing-hash failure.

Written by the indexing model from the issue text.