bash: add HEAD

Closes Homebrew/homebrew#22080.

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

Formula/bash.rb

@@ -7,6 +7,8 @@ class Bash < Formula
   sha256 'a27a1179ec9c0830c65c6aa5d7dab60f7ce1a2a608618570f96bfa72e95ab3d8'
   version '4.2.45'
 
+  head 'git://git.savannah.gnu.org/bash.git'
+
   depends_on 'readline'
 
   # Vendor the patches. The mirrors are unreliable for getting the patches,
@@ -14,7 +16,7 @@ class Bash < Formula
   # patches can be found in: http://ftpmirror.gnu.org/bash/bash-4.2-patches
   def patches
     { :p0 => "https://gist.github.com/jacknagel/4008180/raw/1509a257060aa94e5349250306cce9eb884c837d/bash-4.2-001-045.patch" }
-  end
+  end unless build.head?
 
   def install
     system "./configure", "--prefix=#{prefix}", "--with-installed-readline"