[gnome-sdk-images/gnome-3-26] Update to WebKitGTK+ 2.18.4

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 6bd533e0d631b169a44923d340af2afceb85644e
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Tue Dec 19 10:55:12 2017 -0600

    Update to WebKitGTK+ 2.18.4

 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 55708a0..f4cccfe 100644
--- a/org.gnome.Sdk.json.in
+++ b/org.gnome.Sdk.json.in
@@ -621,8 +621,8 @@
             "sources": [
                 {
                     "type": "archive",
-                    "url": "https://webkitgtk.org/releases/webkitgtk-2.18.3.tar.xz";,
-                    "sha256": "e15420e1616a6f70f321541d467af5ca285bff66b1e0fa68a01df3ccf1b18f9e"
+                    "url": "https://webkitgtk.org/releases/webkitgtk-2.18.4.tar.xz";,
+                    "sha256": "87b6bb9a6065b949ecbe6191313c43e57ad28efdf1f2b5e763405093520632b8"
                 },
                 {
                     "type": "patch",