rmdirSync doesn't throw on non-empty directory

[DanielSWolf]

The original Node implementation of rmdirSync throws an error if the directory is not empty. The implementation in memory-fs quietly deletes the directory an all its contents. rmdirSync effectively behaves like rmdirpSync should.

This is a problem when using memory-fs to mock the native file system and trusting that it behaves similarly.

const MemoryFileSystem = require('memory-fs');

const fs = new MemoryFileSystem();
fs.mkdirpSync('/a/b/c');
fs.rmdirSync('/a/b'); // This should fail. b is not empty.
console.log(fs.readdirSync('/a')); // Empty