Open homebrew version of emacs instead of Apple version
The problem was that emacs was still hashed, so the old version was used even after installing the new one.
Therefore,

$ type emacs
emacs is hashed (/usr/bin/emacs)


This can be remedied by either logging out and then back in again, or forcing the shell to rehash by running hashemacs, which will result in 

$ type emacs
emacs is hashed (/usr/local/bin/emacs)


Then, the correct version will be used.