Replace Vim with nano

The default keymap used in Oh My Zsh is Emacs. As such, the editor
should not be set to Vim. Unfortunately, the editor cannot be set to
Emacs because it is not always installed by default.

Set the default editor to nano.

templates/zshenv

@@ -56,8 +56,8 @@ if [[ -z "$LANG" ]]; then
 fi
 
 # Editors
-export EDITOR="vim"
-export VISUAL="vim"
+export EDITOR='nano'
+export VISUAL='nano'
 export PAGER='less'
 
 # Browser (Default)