fixed json typo

Author: Silberengel

A4.md

@@ -77,7 +77,7 @@ Ideally, citations SHOULD be documented ex-event, within the following structure
     ["version", "<version or edition of the publication>"],
     ["location", "<where was it written or published>"],
     ["g", "<geohash of the precise location>"],
-    ["open_timestamp"], "<`e` tag of kind 1040 event>"],
+    ["open_timestamp", "<`e` tag of kind 1040 event>"],
     ["summary", "<short explanation of which topics the citation covers>"]
   ],
   "content": "<text cited>"