Warning when installing on with yarn

[guidanoli]

When running with yarn 1.22.22...

yarn global add @guidanoli/cmioc

I get this error...

warning @guidanoli/cmioc@0.1.3: The engine "pnpm" appears to be invalid.

This appears to have been fixed in yarn v2, and is a no-fix in v1.
We could remove pnpm from the list of engines to avoid this warning.
It's not like pnpm is necessary to install the package. One can use npm or yarn.

[guidanoli]

Fixed by #11