chore: fix config doc

etc/emqx.conf

@@ -450,8 +450,8 @@ log.file = emqx.log
 
 ## Log to single line
 ## Value: formatter_default | true | false
-## 'default' is equivalent to 'true' when use_json_formatter is 'true'
-## 'default' is equivalent to 'false' when `use_json_formatter is 'false'
+## 'formatter_default' is equivalent to 'true' when log.formatter is 'json'
+## 'formatter_default' is equivalent to 'false' when log.formatter is 'text'
 #log.single_line = formatter_default
 
 ## Enables the log rotation.

src/emqx_logger_jsonfmt.erl

@@ -25,7 +25,7 @@
 %% e.g. logger:log(info, _Data = #{foo => bar}, _Meta = #{metaf1 => 2})
 %% will results in a JSON object look like below:
 %%
-%% {"time": 1620226963427808, "level": "info", msg": "foo: bar", "metaf1": 2}
+%% {"time": 1620226963427808, "level": "info", "msg": "foo: bar", "metaf1": 2}
 
 -module(emqx_logger_jsonfmt).