[gnome-sdk-images] Update to WebKitGTK+ 2.20

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 52d2507a0efdd597e7709e10779e3f87149b0d67
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Mon Mar 12 10:09:52 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 12c3b97..675dcdb 100644
--- a/org.gnome.Sdk.json.in
+++ b/org.gnome.Sdk.json.in
@@ -796,8 +796,8 @@
             "sources": [
                 {
                     "type": "archive",
-                    "url": "https://webkitgtk.org/releases/webkitgtk-2.19.92.tar.xz";,
-                    "sha256": "22b79a525376d09e7a6acc8becffabbac1759906592375767216b9b2c0d871e8"
+                    "url": "https://webkitgtk.org/releases/webkitgtk-2.20.0.tar.xz";,
+                    "sha256": "57f640f720bd9a8a7207f3321cf803a15c2f207b4e7b75ff1be17bc1eeb00a3c"
                 }
             ]
         },