Modify access rules

project.config

diff --git a/project.config b/project.config
index e3c71e4..53e2c65 100644
--- a/project.config
+++ b/project.config
@@ -12,7 +12,7 @@
 	read = group Anonymous Users
 [access "refs/for/refs/*"]
 	push = group Registered Users
-	pushMerge = group Registered Users
+	pushMerge = block group Registered Users
 [access "refs/heads/*"]
 	create = group Administrators
 	create = group Project Owners