async enableFlag (flag) {
    this._enabledFlags = this._enabledFlags | flag

    if (!this._isOpen) {
      return
    }

    this.sendEnabledFlags()
    return this._getEventPromise(this._getConfigEventKey(flag))
  }
Enables a configuration flag.

@param {number} flag - flag to update, as numeric value
@returns {Promise} p
@see WSv2#flags
@example
const ws = new WSv2()

ws.on('open', async () => {
  await ws.enableFlag(WSv2.flags.CHECKSUM)
  console.log('ob checkums enabled')
})

await ws.open()