pipeline: outputs: standard-output: add missing comma (#1355)

Signed-off-by: John Sammut <[email protected]>

Author: jsammut1976

pipeline/outputs/standard-output.md

@@ -6,7 +6,7 @@ The **stdout** output plugin allows to print to the standard output the data rec
 
 | Key | Description | default |
 | :--- | :--- | :--- |
-| Format | Specify the data format to be printed. Supported formats are _msgpack_ _json_, _json\_lines_ and _json\_stream_. | msgpack |
+| Format | Specify the data format to be printed. Supported formats are _msgpack_, _json_, _json\_lines_ and _json\_stream_. | msgpack |
 | json\_date\_key | Specify the name of the time key in the output record. To disable the time key just set the value to `false`. | date |
 | json\_date\_format | Specify the format of the date. Supported formats are _double_, _epoch_, _iso8601_ (eg: _2018-05-30T09:39:52.000681Z_) and _java_sql_timestamp_ (eg: _2018-05-30 09:39:52.000681_) | double |
 | Workers | Enables dedicated thread(s) for this output. Default value is set since version 1.8.13. For previous versions is 0. | 1 |