emacs: make the "emacs" wrapper call its binary with "exec"

This prevents leaving around a lingering bash process whenever
/usr/local/bin/emacs is invoked.

Closes Homebrew/homebrew#32301.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/emacs.rb

@@ -123,7 +123,7 @@ class Emacs < Formula
       (bin/"emacs").unlink # Kill the existing symlink
       (bin/"emacs").write <<-EOS.undent
         #!/bin/bash
-        #{prefix}/Emacs.app/Contents/MacOS/Emacs -nw  "$@"
+        exec #{prefix}/Emacs.app/Contents/MacOS/Emacs -nw  "$@"
       EOS
     else
       if build.with? "x"