[gnome-sdk-images] Upgrade to WebKitGTK+ 2.21.5

[Michael Catanzaro <mcatanzaro src gnome org>]

commit f14d695ff853fdfe1a92179c1275e0bb9ddcc98c
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Fri Jul 20 06:45:15 2018 -0500

    Upgrade to WebKitGTK+ 2.21.5

 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 510535d..1814105 100644
--- a/org.gnome.Sdk.json.in
+++ b/org.gnome.Sdk.json.in
@@ -890,8 +890,8 @@
             "sources": [
                 {
                     "type": "archive",
-                    "url": "https://webkitgtk.org/releases/webkitgtk-2.21.4.tar.xz";,
-                    "sha256": "59f4359ace702ecaa92b975666c1bcde3858258909b047e7675ce3807efdd1e7"
+                    "url": "https://webkitgtk.org/releases/webkitgtk-2.21.5.tar.xz";,
+                    "sha256": "c31ec8c701dc174a6898fc78f08b549ec986abb5e6c7e86db46680a9ee45821f"
                 }
             ]
         },