title: pyplot does not have attribute 'xaxis_set_major_formatter'
body: <p>I am trying to plot hours in the x-axis [in this picture] using this code </p>
  
  <pre><code>#create a lineplot
  fig = plt.figure(figsize=(20,5))
  ax = fig.add_subplot()
  plt.title('SUBIC-NAIA Air Temp Difference. (C)')
  ax.plot(date_rng,NASU_dif)
  monthyearFmt = mdates.DateFormatter('%Y-%m-%d-%h')
  plt.xaxis_set_major_formatter(monthyearFmt)
  plt.xlabel('Time Step (hr)')
  plt.ylabel('Air Temperature (m/s)')
  plt.legend(loc='upper right', prop={'size': 10})
  plt.show()
  </code></pre>
  
  <p>but I am receiving</p>
  
  <blockquote>
    <p>AttributeError: module 'matplotlib.pyplot' has no attribute
    'xaxis_set_major_formatter'</p>
  </blockquote>
  
  <p>I have a daterng as my index. How do I solve this one?</p>
  
  <blockquote>
    <p>DatetimeIndex(['2018-04-22 00:00:00', '2018-04-22 01:00:00',
                   '2018-04-22 02:00:00', '2018-04-22 03:00:00',
                   '2018-04-22 04:00:00', '2018-04-22 05:00:00',
                   '2018-04-22 06:00:00', '2018-04-22 07:00:00',
                   '2018-04-22 08:00:00', '2018-04-22 09:00:00',
                   ...
                   '2018-04-29 15:00:00', '2018-04-29 16:00:00',
                   '2018-04-29 17:00:00', '2018-04-29 18:00:00',
                   '2018-04-29 19:00:00', '2018-04-29 20:00:00',
                   '2018-04-29 21:00:00', '2018-04-29 22:00:00',
                   '2018-04-29 23:00:00', '2018-04-30 00:00:00'],
                  dtype='datetime64[ns]', length=193, freq='H')</p>
  </blockquote>