Remove mkdirp dependency

[MasterOdin]

Closes #163

PR removes the mkdirp dependency relying on { recursive: true } for fs.mkdir which has the same behavior. This necessitated bumping the supported node version to 10.12 as that's the version of Node that added this feature.

Note, I did not remove the recursive folder removal in the socket test (https://github.com/node-portfinder/node-portfinder/blob/b64ab4f707fccc079da3f86716ec0c78be61a30b/test/port-finder-socket.test.js#L68-L76) as recursive was added to fs.rmdir in 12.10, and then they deprecated that option and added the fs.rm function in 14.14.

[eriktrom]

Awesome, thanks!

[eriktrom]

Note, I did not remove the recursive folder removal in the socket test (https://github.com/node-portfinder/node-portfinder/blob/b64ab4f707fccc079da3f86716ec0c78be61a30b/test/port-finder-socket.test.js#L68-L76) as recursive was added to fs.rmdir in 12.10, and then they deprecated that option and added the fs.rm function in 14.14.

Thanks for being so careful 👍