openlp: update livecheck to ignore rc release

Signed-off-by: Rui Chen <rui@chenrui.dev>

Casks/o/openlp.rb

@@ -9,7 +9,7 @@ cask "openlp" do
 
   livecheck do
     url "https://get.openlp.org"
-    regex(/href=['"]?(\d+(?:\.\d+)+)['"]?/i)
+    regex(%r{href=['"]?(\d+(?:\.\d+)+)(?!rc\d+)/['"]?}i)
   end
 
   app "OpenLP.app"