Prevents oh-my-zsh loading the .zshenv twice

oh-my-zsh.sh

 # Check for updates on initial load...
 if [ "$DISABLE_AUTO_UPDATE" != "true" ]; then
-  /usr/bin/env ZSH=$ZSH DISABLE_UPDATE_PROMPT=$DISABLE_UPDATE_PROMPT zsh $ZSH/tools/check_for_upgrade.sh
+  /usr/bin/env ZSH=$ZSH DISABLE_UPDATE_PROMPT=$DISABLE_UPDATE_PROMPT zsh -f $ZSH/tools/check_for_upgrade.sh
 fi
 
 # Initializes Oh My Zsh