updates readme

README.md

@@ -1,7 +1,7 @@
 # Laravel Etag Middleware for JSON APIs
 This a middleware specifically for the Laravel framework and __RESTful APIs__ build with it.
 It hashaes the response content and adds it to ETag header of HTTP response.
-Then it listenes to __If-Match__ and __If-Not-Match__ headers of the requests that expect to
+Then it listenes to __If-Match__ and __If-None-Match__ headers of the requests that expect to
 receive json in response in order to see if a new content needs to be delivered or just 304 Not Modified response is sufficient.
 
 ## Author