.zshrc: Add variables to tweak Homebrew behavior

Homebrew runs `brew update` before every fucking brew command? No
thank you. Also, after reading `man brew` I found there are some
other options to tweak for security and performance, like disallowing
HTTPS→HTTP redirects and using less cores to compile stuff (running
four make jobs on a system with two real cores? WTF, Homebrew?).

.zshrc

@@ -29,6 +29,11 @@ if [[ "$OSTYPE" =~ ^darwin.*$ ]]; then
     # opt out of Homebrew analytics
     # see: https://github.com/Homebrew/brew/blob/master/share/doc/homebrew/Analytics.md
     export HOMEBREW_NO_ANALYTICS=1
+    export HOMEBREW_NO_AUTO_UPDATE=1
+    export HOMEBREW_NO_EMOJI=1
+    export HOMEBREW_NO_INSECURE_REDIRECT=1
+    export HOMEBREW_MAKE_JOBS=3
+    export HOMEBREW_NO_AUTO_UPDATE=1
 
     # pass needs umount and diskutil, which are in /sbin and /usr/sbin
     PATH=$PATH:/sbin:/usr/sbin