tig: add zsh completion

See also jonas/tig#433

Closes #43421.

Signed-off-by: Alex Dunn <dunn.alex@gmail.com>

Library/Formula/tig.rb

@@ -3,6 +3,18 @@ class Tig < Formula
   homepage "http://jonas.nitro.dk/tig/"
   url "http://jonas.nitro.dk/tig/releases/tig-2.1.1.tar.gz"
   sha256 "50c5179fd564b829b6b2cec087e66f10cf8799601de19350df0772ae77e4852f"
+  head "https://github.com/jonas/tig.git"
+
+  stable do
+    url "http://jonas.nitro.dk/tig/releases/tig-2.1.1.tar.gz"
+    sha256 "50c5179fd564b829b6b2cec087e66f10cf8799601de19350df0772ae77e4852f"
+
+    # Merged in HEAD; remove in next stable release
+    patch do
+      url "https://github.com/jonas/tig/commit/91912eb97da4f6907015dab41ef9bba315730854.diff"
+      sha256 "263e86b25f788eb158bdd667e112bc839debe9e3fe788cbc39cc9654b65b6c8a"
+    end
+  end
 
   bottle do
     cellar :any
@@ -32,5 +44,7 @@ def install
     system "make", "install"
     system "make install-doc-man" if build.with? "docs"
     bash_completion.install "contrib/tig-completion.bash"
+    zsh_completion.install "contrib/tig-completion.zsh" => "_tig"
+    cp "#{bash_completion}/tig-completion.bash", zsh_completion
   end
 end