[gnome-sdk-images] Update webkitgtk4 to version 2.17.4

[Adrien Plazas <aplazas src gnome org>]

commit af646f248ec75a94465ec1cb07dbdc599ea913f5
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Wed Jul 12 10:28:26 2017 +0200

    Update webkitgtk4 to version 2.17.4

 org.gnome.Sdk.json.in |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/org.gnome.Sdk.json.in b/org.gnome.Sdk.json.in
index ed5f308..5ff991a 100644
--- a/org.gnome.Sdk.json.in
+++ b/org.gnome.Sdk.json.in
@@ -784,8 +784,8 @@
             "sources": [
                 {
                     "type": "archive",
-                    "url": "https://webkitgtk.org/releases/webkitgtk-2.17.3.tar.xz";,
-                    "sha256": "79f168c30953dbd273f984d3cc85482169e6822fcf7cf0031c86cf8aa1816b35"
+                    "url": "https://webkitgtk.org/releases/webkitgtk-2.17.4.tar.xz";,
+                    "sha256": "a497eb3c1a8cbc78ccdeb6d7d22557a33ae879e80521d968eaa095a62c9f8526"
                 },
                 {
                     "type": "patch",