Update links in fluentd input readme (influxdata#6175)

plugins/inputs/fluentd/README.md

@@ -1,10 +1,10 @@
 # Fluentd Input Plugin
 
-The fluentd plugin gathers metrics from plugin endpoint provided by [in_monitor plugin](http://docs.fluentd.org/v0.12/articles/monitoring).
+The fluentd plugin gathers metrics from plugin endpoint provided by [in_monitor plugin](https://docs.fluentd.org/input/monitor_agent).
 This plugin understands data provided by /api/plugin.json resource (/api/config.json is not covered).
 
 You might need to adjust your fluentd configuration, in order to reduce series cardinality in case your fluentd restarts frequently. Every time fluentd starts, `plugin_id` value is given a new random value.
-According to [fluentd documentation](http://docs.fluentd.org/v0.12/articles/config-file), you are able to add `@id`  parameter for each plugin to avoid this behaviour and define custom `plugin_id`.
+According to [fluentd documentation](https://docs.fluentd.org/configuration/config-file#common-plugin-parameter), you are able to add `@id`  parameter for each plugin to avoid this behaviour and define custom `plugin_id`.
 
 example configuration with `@id` parameter for http plugin:
 ```