Plot the time series.

def plot(self, label=None, colour='g', style='-'): # pragma: no cover
        '''Plot the time series.'''
        pylab = LazyImport.pylab()
        pylab.plot(self.dates, self.values, '%s%s' % (colour, style), label=label)
        if label is not None:
            pylab.legend()
        pylab.show()