fix typo on binary_mnist_datamodule

thanks @akihironitta

Co-authored-by: Akihiro Nitta <nitta@akihironitta.com>

pl_bolts/datamodules/binary_mnist_datamodule.py

@@ -118,7 +118,7 @@ def train_dataloader(self):
         )
         return loader
 
-    def val_dataloader(self,):
+    def val_dataloader(self):
         """
         MNIST val set uses a subset of the training set for validation
         """