imageio uninstall issue while installing CREPE via pip

[jongwook]

At least in Ubuntu bionic (18.04) and pip 9.x, I see

DEPRECATION: Uninstalling a distutils installed project (imageio) has been deprecated and will be removed in a future version. This is due to the fact that uninstalling a distutils project will only partially uninstall the project.

and in pip 10, the installation fails because of this.

We need a way to not trigger the uninstallation of imageio

[justinsalamon]

Related, I still think the core library shouldn't have any image/plotting dependencies, and their loading can be optional (along the lines of librosa.display).