function onGlob( error, files ) {
		if ( error ) {
			debug( 'Encountered an error when searching for files: %s', error.message );
			return done( error );
		}
		debug( 'Found %d files.', files.length );
		if ( files.length ) {
			debug( 'Processing files.' );
			linter( files, done );
		} else {
			done( null, null );
		}
	}
Callback invoked after matching files.

@private
@param {(Error|null)} error - error object
@param {StringArray} files - list of matching files
@returns {void}