resume(val) {
    if (!this.parent) {
      return this;
    }
    val = val || '';
    if (!this._activePrompt) {
      return this;
    }
    if (this._midPrompt) {
      return this;
    }
    const rl = this._activePrompt.screen.rl;
    rl.output.write(val);
    this._midPrompt = true;
    return this;
  }
Resumes active prompt, accepting
a string, which will fill the prompt
with that text and put the cursor at
the end.

@param {String} val
@api public