Set xaxis limits

        Parameters
        ----------
        low : number
        high : number

        Returns
        -------
        Chart

def xlim(self, low, high):
        """Set xaxis limits

        Parameters
        ----------
        low : number
        high : number

        Returns
        -------
        Chart

        """
        self.chart['xAxis'][0]['min'] = low
        self.chart['xAxis'][0]['max'] = high
        return self