Updated Upgrading to Guard 2.0 (markdown)

Upgrading-to-Guard-2.0.md

@@ -72,10 +72,10 @@ end
 
 Notifiers are now classes with a common interface inherited from `Guard::Notifier::Base`:
 
-* [require] `#notify(message, opts = {})`
-* [optional] `.supported_hosts`
-* [optional] `.available?(opts = {})`
-* [optional] `.gem_name`
+* _[required]_ `#notify(message, opts = {})`
+* _[optional]_ `.supported_hosts`
+* _[optional]_ `.available?(opts = {})`
+* _[optional]_ `.gem_name`
 
 **Breaking change:** The signature of `#notify` in the notifiers has changed from `#notify(type, title, message, image, options = {})` to `notify(message, opts = {})` (`:type`, `:title` and `:image` must now be passed in the `opts` hash.