gnome3.webkitgtk: 2.20.2 -> 2.20.3

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/webkitgtk/versions.

These checks were done:

- built on NixOS
- /nix/store/kg4axk1r8r3lw4hidrb639lvnhidkmg1-webkitgtk-2.20.3/bin/WebKitWebDriver passed the binary check.
- 1 of 1 passed binary check by having a zero exit code.
- 0 of 1 passed binary check by having the new version present in output.
- found 2.20.3 with grep in /nix/store/kg4axk1r8r3lw4hidrb639lvnhidkmg1-webkitgtk-2.20.3
- directory tree listing: https://gist.github.com/9bcce0d9c55941e792a46ccc39ce7efb
- du listing: https://gist.github.com/79054d0bb16c7cff8f636f5af11a2408

pkgs/development/libraries/webkitgtk/2.20.nix

@@ -15,7 +15,7 @@ assert stdenv.isDarwin -> !enableGtk2Plugins;
 with stdenv.lib;
 stdenv.mkDerivation rec {
   name = "webkitgtk-${version}";
-  version = "2.20.2";
+  version = "2.20.3";
 
   meta = {
     description = "Web content rendering engine, GTK+ port";
@@ -28,7 +28,7 @@ stdenv.mkDerivation rec {
 
   src = fetchurl {
     url = "http://webkitgtk.org/releases/${name}.tar.xz";
-    sha256 = "1qi6nnj4qidzija1am9xscwjxwfqwhiy7x39ndriqgzh86i97znz";
+    sha256 = "1n0dy94bm7wvxln4jis1gp8plv8n4a01g41724zsf5psg1yk16sp";
   };
 
   patches = optionals stdenv.isDarwin [