Update mac.md (#1573)

Fix permalink to `#mac-pip`

Author: yyolk

_get_started/installation/mac.md

@@ -63,7 +63,7 @@ conda install pytorch torchvision -c pytorch
 ```
 
 ### pip
-{: #mac-anaconda}
+{: #mac-pip}
 
 To install PyTorch via pip, use one of the following two commands, depending on your Python version: