Fix brew upgrade command (#19)

I typed `$ brew upgrade —all` in Terminal and got this: ``` Warning: We decided to not change the behaviour of `brew upgrade` so `brew upgrade --all` is equivalent to `brew upgrade` without any other arguments (so the `--all` is a no-op and can be removed). ```
brainix · Oct 3, 2016 · 5e90e3a · 5e90e3a
1 parent 0f47711
commit 5e90e3a
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/Makefile b/Makefile
@@ -36,7 +36,7 @@ python:
 
 upgrade:
 	brew update
-	brew upgrade --all
+	brew upgrade
 	brew cleanup
 	pyenv rehash
 	pip3 install --upgrade pip