BUG : fixes whis over-writing in boxplot_stats

Restore the value of `whis` to the input value at the top of each pass
through the for-loop.

@WeatherGod hit the nail on the head.

closes #3468

lib/matplotlib/cbook.py

@@ -1954,11 +1954,15 @@ def _compute_conf_interval(data, med, iqr, bootstrap):
     elif len(labels) != ncols:
         raise ValueError("Dimensions of labels and X must be compatible")
 
+    input_whis = whis
     for ii, (x, label) in enumerate(zip(X, labels), start=0):
         # empty dict
         stats = {}
         stats['label'] = label
 
+        # restore whis incase in got changed
+        whis = input_whis
+
         # arithmetic mean
         stats['mean'] = np.mean(x)