Emacs: fix confusing phrasing in readme

Someone thought the Emacs plugin readme was referring to Emacs version
31 or newer. (The latest Emacs version is 28, so this makes no sense.)
Reword to avoid confusion.

Author: strager

plugin/emacs/README.md

@@ -12,7 +12,7 @@ work.
 Flycheck plugin must be installed and configured in order for this plugin to
 work:
 
-* [Flycheck] - On the fly syntax checking for GNU Emacs 31 or newer
+* [Flycheck] - On the fly syntax checking, version 31 or newer
 
 ## Installation