DOC: fix plot in missing data section, close #1827

Author: lodagro

doc/source/missing_data.rst

@@ -239,11 +239,8 @@ interpolation assumes equally spaced points.
    ts.interpolate().head()
 
    @savefig series_interpolate.png width=6in
-   fig = plt.figure()
    ts.interpolate().plot()
 
-   plt.close('all')
-
 Index aware interpolation is available via the ``method`` keyword:
 
 .. ipython:: python