(DOCSP-16159): Add missing comma to datefromstring example

Author: jeff-allen-mongo

source/reference/operator/aggregation/dateFromString.txt

@@ -93,7 +93,7 @@ Consider a collection ``logmessages`` that contains the following documents:
    { _id: 1, date: "2017-02-08T12:10:40.787", timezone: "America/New_York", message:  "Step 1: Started" },
    { _id: 2, date: "2017-02-08", timezone: "-05:00", message:  "Step 1: Ended" },
    { _id: 3, message:  " Step 1: Ended " },
-   { _id: 4, date: "2017-02-09", timezone: "Europe/London", message: "Step 2: Started"}
+   { _id: 4, date: "2017-02-09", timezone: "Europe/London", message: "Step 2: Started"},
    { _id: 5, date: "2017-02-09T03:35:02.055", timezone: "+0530", message: "Step 2: In Progress"}
 
 The following aggregation uses $dateFromString to convert the ``date`` value