Remove extraneous comma from m.presence schema

This causes the build to fail. Fixes #1146

Signed-off-by: Travis Ralston <travpc@gmail.com>

event-schemas/examples/m.presence

@@ -3,7 +3,7 @@
     "avatar_url": "mxc://localhost:wefuiwegh8742w",
     "last_active_ago": 2478593,
     "presence": "online",
-    "currently_active": false,
+    "currently_active": false
   },
   "sender": "@example:localhost",
   "type": "m.presence"