fix: clean up env directory after failure

[richardlau]

If a module fails to install, clean up the env directory before
attempting the next module.

[richardlau]

I've pushed this up as-is as it is the end of my working day. I'd like to add a test for this somehow.

[helio-frota]

I think for this specific case that is enough since the cleanEnvDirectory is already covered by tests
it('should clean the npcheck-env directory', () => {...

Also npcheck has no cli.js test yet, and creating a test for this also means checking the error messages and etc.
For example to validate error messages like this:

`Module "${pkgInfo.name}" couldn't be installed. Check ${logs} for more information.`

ofc is doable but I don't think that should be done now to cover that change on cli.js 👍