function reDirnamePosix() {
	return /^((?:\.(?![^\/]))|(?:(?:\/?|)(?:[\s\S]*?)))(?:\/+?|)(?:(?:\.{1,2}|[^\/]+?|)(?:\.[^.\/]*|))(?:[\/]*)$/; // eslint-disable-line no-useless-escape
}
Returns a regular expression to capture a POSIX path dirname.

@returns {RegExp} regular expression

@example
var RE_DIRNAME_POSIX = reDirnamePosix();
var dir = RE_DIRNAME_POSIX.exec( 'foo/bar/index.js' )[ 1 ];
// returns 'foo/bar'