delay(opts) {
    let headDelay
    let bodyDelay
    if (typeof opts === 'number') {
      headDelay = opts
      bodyDelay = 0
    } else if (typeof opts === 'object') {
      headDelay = opts.head || 0
      bodyDelay = opts.body || 0
    } else {
      throw new Error(`Unexpected input opts ${opts}`)
    }

    return this.delayConnection(headDelay).delayBody(bodyDelay)
  }
Delay the response by a certain number of ms.

@param {(integer|object)} opts - Number of milliseconds to wait, or an object
@param {integer} [opts.head] - Number of milliseconds to wait before response is sent
@param {integer} [opts.body] - Number of milliseconds to wait before response body is sent
@return {Interceptor} - the current interceptor for chaining