installing.md: update homebrew instructions
It appears that the fuse tap was deprecated:
@@ -147,7 +147,7 @@ First, handle prerequisites:
Afterward, gcsfuse can be installed with `brew`:
- brew install homebrew/fuse/gcsfuse
+ brew install gcsfuse
sudo ln -s /usr/local/sbin/mount_gcsfuse /sbin # For mount(8) support
The second command is only necessary if you want to use gcsfuse with the
