[gnome-sdk-images/gnome-3-26] Update to WebKitGTK+ 2.20

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 0c6730fd4d304a9a269e8a4a0380423c1dc88502
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Mon Mar 12 10:16:57 2018 -0500

    Update to WebKitGTK+ 2.20

 org.gnome.Sdk.json.in | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/org.gnome.Sdk.json.in b/org.gnome.Sdk.json.in
index 8e7de00..6c9c096 100644
--- a/org.gnome.Sdk.json.in
+++ b/org.gnome.Sdk.json.in
@@ -638,8 +638,8 @@
             "sources": [
                 {
                     "type": "archive",
-                    "url": "https://webkitgtk.org/releases/webkitgtk-2.18.6.tar.xz";,
-                    "sha256": "93912cc2f40f12e452be1ca4babdbdaac0ec4f828d441257a6b06c2963bbac3c"
+                    "url": "https://webkitgtk.org/releases/webkitgtk-2.20.0.tar.xz";,
+                    "sha256": "57f640f720bd9a8a7207f3321cf803a15c2f207b4e7b75ff1be17bc1eeb00a3c"
                 },
                 {
                     "type": "patch",