Update GNOME runtime and move to rolling release of openjdk

This wasn't possible before because my version of flatpak was buggy.

app.briar.gtk.json

 {
     "app-id": "app.briar.gtk",
     "runtime": "org.gnome.Platform",
-    "runtime-version": "3.32",
+    "runtime-version": "3.36",
     "sdk": "org.gnome.Sdk",
     "sdk-extensions": [
-        "org.freedesktop.Sdk.Extension.openjdk11"
+        "org.freedesktop.Sdk.Extension.openjdk"
     ],
     "command": "briar-gtk",
     "finish-args": [
@@ -42,7 +42,7 @@
             "name": "openjdk",
             "buildsystem": "simple",
             "build-commands": [
-                "/usr/lib/sdk/openjdk11/install.sh"
+                "/usr/lib/sdk/openjdk/install.sh"
             ]
         },
         {