Fix error in docstring example

Author: mdpiper

lessons/python/ivy_diffusion/diffusion.py

@@ -14,16 +14,16 @@ class Diffusion:
     >>> m.concentration = np.zeros(m.shape)
     >>> m.concentration[int(m.shape/2)] = 5
     >>> m.concentration
-    array([  0.0,   0.0,   0.0,   0.0,   0.0,   5.0,   0.0,   0.0,   0.0,
-             0.0])
+    array([   0.0,    0.0,    0.0,    0.0,    0.0,    5.0,    0.0,    0.0,
+              0.0,    0.0])
     >>> m.time
     0.0
     >>> m.update()
     >>> m.time
     1.0
     >>> m.concentration
-    array([  0.0,   0.0,   0.0,   0.0,   1.2,   2.5,   1.2,   0.0,   0.0,
-             0.0])
+    array([   0.0,    0.0,    0.0,    0.0,    1.2,    2.5,    1.2,    0.0,
+              0.0,    0.0])
     """
 
     def __init__(self, shape=10, spacing=1.0, diffusivity=1.0):