Fix a typo

Closes #13

Signed-off-by: Hiroshi Hatake <hatake@calyptia.com>

README.md

@@ -1432,7 +1432,7 @@ Specify AWS OpenSearch Service endpoint.
 </endpoint>
 ```
 
-**NOTE:** This plugin will remove trailing slashes automatically. You don't need to pay attension to the trailing slash characters.
+**NOTE:** This plugin will remove trailing slashes automatically. You don't need to pay attention to the trailing slash characters.
 
 #### access_key_id