z.rb: append the missing 'h', correct the indent.

Closes Homebrew/homebrew#16998.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/z.rb

@@ -14,20 +14,20 @@ class Z < Formula
 
   def caveats; <<-EOS.undent
     For Bash or Zsh, put something like this in your $HOME/.bashrc or $HOME/.zshrc:
-      . `brew --prefix`/etc/profile.d/z.s
+      . `brew --prefix`/etc/profile.d/z.sh
 
     ZSH USERS BACKWARD COMPATIBILITY WARNING:
      z now handles 'precmd' set up for zsh. z (<=1.3) users using zsh should
      remove the precmd function that was described in the installation
      instructions for previous versions.
 
-   In short, this:
+    In short, this:
       . /path/to/z.sh
       function precmd () {
        _z --add "$(pwd -P)"
       }
 
-   should now be:
+    should now be:
       . `brew --prefix`/etc/profile.d/z.sh
     EOS
   end