watch file for changes
function watch(file) {
      if (!~extensions.indexOf(extname(file))) return;
      fs.watchFile(file, { interval: interval }, function(curr, prev){
        if (curr.mtime > prev.mtime) {
          console.log('  \033[36mchanged\033[0m \033[90m- %s\033[0m', file);
          master.restartWorkers(signal);
        }
      });
    }