Updated options params index [max_tokens] to [max_output_tokens] #33

[techmahedy]

Previous:

 /**
   * Set max tokens
   *
   * @param int $tokens
   * @return self
   */
  public function maxTokens(int $tokens): self
  {
      $this->params['max_tokens'] = $tokens;

      return $this;
  }

Now:

 /**
   * Set max tokens
   *
   * @param int $tokens
   * @return self
   */
  public function maxTokens(int $tokens): self
  {
      $this->params['max_output_tokens'] = $tokens;

      return $this;
  }

Now this is compatible with symfony v0.1 version.