src/Http.php
public function header($key, $value = null) {
        if (is_array($key)) {
            return $this->setHeader($key);
        }
        return $this->setHeader([
            $key => $value
        ]);
    }
public function header($key, $value = null) {
        if (is_array($key)) {
            return $this->setHeader($key);
        }
        return $this->setHeader([
            $key => $value
        ]);
    }
设置请求头
@param $key
@param null $value
@return Http