Docs: Update automatic_retries description (logstash-plugins#104)

Author: sonnhotani

docs/index.asciidoc

@@ -86,7 +86,7 @@ output plugins.
 
 How many times should the client retry a failing URL. We highly recommend NOT setting this value
 to zero if keepalive is enabled. Some servers incorrectly end keepalives early requiring a retry!
-Note: if `retry_non_idempotent` is set only GET, HEAD, PUT, DELETE, OPTIONS, and TRACE requests will be retried.
+Note: if `retry_non_idempotent` is NOT set only GET, HEAD, PUT, DELETE, OPTIONS, and TRACE requests will be retried.
 
 [id="plugins-{type}s-{plugin}-cacert"]
 ===== `cacert` 
@@ -384,4 +384,4 @@ See https://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache
 [id="plugins-{type}s-{plugin}-common-options"]
 include::{include_path}/{type}.asciidoc[]
 
-:default_codec!:
+:default_codec!: