Fix Image Tutorial: plt.imshow instead of mpimg.imshow.

Author: mgiuca-google

doc/users/image_tutorial.rst

@@ -337,7 +337,7 @@ and the computer has to draw in pixels to fill that space.
     In [9]: img = Image.open('stinkbug.png')    # Open image as PIL image object
     In [10]: rsize = img.resize((img.size[0]/10,img.size[1]/10)) # Use PIL to resize
     In [11]: rsizeArr = np.asarray(rsize)  # Get array back
-    In [12]: imgplot = mpimg.imshow(rsizeArr)
+    In [12]: imgplot = plt.imshow(rsizeArr)
 
 .. plot::