fix doc build error after #2312 (#2326)

Author: fujiisoup

doc/interpolation.rst

@@ -49,7 +49,7 @@ array-like, which gives the interpolated result as an array.
     da.interp(time=[2.5, 3.5])
 
 
-To interpolate data with a :py:func:`numpy.datetime64` coordinate you have to 
+To interpolate data with a :py:func:`numpy.datetime64` coordinate you have to
 wrap it explicitly in a :py:func:`numpy.datetime64` object.
 
 .. ipython:: python
@@ -58,7 +58,7 @@ wrap it explicitly in a :py:func:`numpy.datetime64` object.
                            [('time', pd.date_range('1/1/2000', '1/3/2000', periods=2))])
     da_dt64.interp(time=np.datetime64('2000-01-02'))
 
-The interpolated data can be merged into the original :py:class:`~xarray.DataArray` 
+The interpolated data can be merged into the original :py:class:`~xarray.DataArray`
 by specifing the time periods required.
 
 .. ipython:: python

xarray/core/dataarray.py

@@ -943,7 +943,7 @@ def interp(self, coords=None, method='linear', assume_sorted=False,
         scipy.interpolate.interpn
 
         Examples
-        -------
+        --------
         >>> da = xr.DataArray([1, 3], [('x', np.arange(2))])
         >>> da.interp(x=0.5)
         <xarray.DataArray ()>