doc: Format example JSON data better

doc/src/sgml/func.sgml

@@ -12822,17 +12822,20 @@ table2-mapping
    For example, suppose you have some JSON data from a GPS tracker that you
    would like to parse, such as:
 <programlisting>
-{ "track" :
 {
+  "track": {
     "segments": [
-      { "location":   [ 47.763, 13.4034 ],
+      {
+        "location":   [ 47.763, 13.4034 ],
         "start time": "2018-10-14 10:05:14",
         "HR": 73
       },
-      { "location":   [ 47.706, 13.2635 ],
+      {
+        "location":   [ 47.706, 13.2635 ],
         "start time": "2018-10-14 10:39:21",
         "HR": 135
-      } ]
+      }
+    ]
   }
 }
 </programlisting>