function WriteStream$open () {
    var that = this
    open(that.path, that.flags, that.mode, function (err, fd) {
      if (err) {
        that.destroy()
        that.emit('error', err)
      } else {
        that.fd = fd
        that.emit('open', fd)
      }
    })
  }
Lookup the MIME type for a file path/extension.

@param {string} path
@return {boolean|string}