Added option for passing alpha to kde in plot_posterior via kwargs

Author: fonnesbeck

pymc3/plots/artists.py

@@ -122,7 +122,11 @@ def set_key_if_doesnt_exist(d, key, value):
             d[key] = value
 
     if kde_plot:
-        kdeplot(trace_values, alpha=0.35, ax=ax, **kwargs)
+        if 'alpha' in kwargs:
+            alpha = kwargs.pop('alpha')
+        else:
+            alpha = 0.35
+        kdeplot(trace_values, alpha=alpha, ax=ax, **kwargs)
 
     else:
         set_key_if_doesnt_exist(kwargs, 'bins', 30)