fixes #3717 (#3741)

Author: aloctavodia

pymc3/smc/smc.py

@@ -427,7 +427,7 @@ def gauss_kernel(self, value):
 
     def absolute_error(self, a, b):
         if self.sum_stat:
-            return np.atleast_2d(np.abs(a.mean() - b.mean()))
+            return np.abs(a.mean() - b.mean())
         else:
             return np.mean(np.atleast_2d(np.abs(a - b)))