Fix typo in DCGAN Tutorial (#2304)

Co-authored-by: Svetlana Karslioglu <svekars@fb.com>

beginner_source/dcgan_faces_tutorial.py

@@ -514,7 +514,7 @@ def forward(self, input):
 # practices shown in `ganhacks <https://github.com/soumith/ganhacks>`__.
 # Namely, we will “construct different mini-batches for real and fake”
 # images, and also adjust G’s objective function to maximize
-# :math:`logD(G(z))`. Training is split up into two main parts. Part 1
+# :math:`log(D(G(z)))`. Training is split up into two main parts. Part 1
 # updates the Discriminator and Part 2 updates the Generator.
 # 
 # **Part 1 - Train the Discriminator**