DOC: fix build errors/warnings

Author: jorisvandenbossche

doc/source/basics.rst

@@ -1725,6 +1725,7 @@ pass ``convert_numeric=True``. This will force strings and numbers alike to be n
 they will be set to ``np.nan``.
 
 .. ipython:: python
+   :okwarning:
 
    df3['D'] = '1.'
    df3['E'] = '1'

doc/source/computation.rst

@@ -267,6 +267,7 @@ sugar for applying the moving window operator to all of the DataFrame's columns:
 
 .. ipython:: python
    :suppress:
+
    plt.close('all')
 
 .. ipython:: python
@@ -541,7 +542,7 @@ which gives
 
 .. math::
 
-    y_t = \frac{x_t + (1 - \alpha)x_{t-1} + (1 - \alpha)^2 x_{t-2} + ... 
+    y_t = \frac{x_t + (1 - \alpha)x_{t-1} + (1 - \alpha)^2 x_{t-2} + ...
     + (1 - \alpha)^t x_{0}}{1 + (1 - \alpha) + (1 - \alpha)^2 + ...
     + (1 - \alpha)^t}
 
@@ -620,7 +621,6 @@ Here is an example for a univariate time series:
 
 .. ipython:: python
 
-   plt.close('all')
    ts.plot(style='k--')
 
    @savefig ewma_ex.png