public function appendPair($key, $value)
    {
        $header = sprintf('%s: %s', $key, $value);
        $this->append($header);

        return $this;
    }
public function appendPair($key, $value)
    {
        $header = sprintf('%s: %s', $key, $value);
        $this->append($header);

        return $this;
    }
public function appendPair ( $ key , $ value ) { $ header = sprintf ( '%s: %s' , $ key , $ value ) ; $ this -> append ( $ header ) ; return $ this ; }
Appends a pair

@param string $key
@param string $value
@return \Krystal\Http\HeaderBag
Appends a pair