Test against npm@7

[rwjblue]

In theory this package should work exactly the same under npm as it does under yarn. We do not currently shell out to yarn at all, we use npm publish to actually publish each package already:

https://github.com/rwjblue/release-it-yarn-workspaces/blob/4480e0bab42b3aab35539bc1e9ee2d3fdc80fec1/index.js#L405

[scalvert]

I don't even know what there would be to test, because all this cares about is that you have a workspaces setup in your project. It looks as though workspaces support in npm 7 works the same as yarn, so I believe this should 'just work'.