DetachedPlugin entry.

(cherry picked from commit e4ba41d539)

core/src/main/java/hudson/ClassicPluginStrategy.java

@@ -272,7 +272,8 @@ public class ClassicPluginStrategy implements PluginStrategy {
         new DetachedPlugin("mailer","1.493.*","1.2"),
         new DetachedPlugin("matrix-auth","1.535.*","1.0.2"),
         new DetachedPlugin("windows-slaves","1.547.*","1.0"),
-        new DetachedPlugin("antisamy-markup-formatter","1.553.*","1.0")
+        new DetachedPlugin("antisamy-markup-formatter","1.553.*","1.0"),
+        new DetachedPlugin("matrix-project","1.561.*","1.0")
     );
 
     /**