Update dependencies

README.md

@@ -13,8 +13,8 @@ Go SDL2 application for Linux.
 sudo dnf install flatpak-builder
 
 # Get the base layers.
-flatpak install flathub org.freedesktop.Sdk//20.08
-flatpak install flathub org.freedesktop.Sdk.Extension.golang//20.08
+flatpak install flathub org.freedesktop.Sdk//21.08
+flatpak install flathub org.freedesktop.Sdk.Extension.golang//21.08
 ```
 
 ## Setup

com.sketchymaze.Doodle.json

@@ -1,7 +1,7 @@
 {
     "app-id": "com.sketchymaze.Doodle",
     "runtime": "org.freedesktop.Platform",
-    "runtime-version": "20.08",
+    "runtime-version": "21.08",
     "sdk": "org.freedesktop.Sdk",
     "sdk-extensions": [
         "org.freedesktop.Sdk.Extension.golang"