title: matplotlib sharex with colorbar not working
body: <p><a href="https://i.stack.imgur.com/zwppo.png" rel="noreferrer"><img src="https://i.stack.imgur.com/zwppo.png" alt="enter image description here"></a>I have 2 subplots- 1 scatter and one bar for which I would like a shared x axis. The scatter plot has a color bar. The sharex doesn't seem to work with this as the axis for the two plots do not coincide. 
  My code:</p>
  
  <pre><code>fig, (ax, ax2) = plt.subplots(2,1, gridspec_kw = {'height_ratios':[13,2]},figsize=(15,12), sharex=True)
  
  df_plotdata.plot(kind='scatter', ax=ax, x='index_cancer', y='index_g', s=df_plotdata['freq1']*50, c=df_plotdata['freq2'], cmap=cmap)
  
  df2.plot(ax=ax2, x='index_cancer', y='freq', kind = 'bar')
  </code></pre>