Immutable private field might as well be final

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/proxy/trunk@1582298 13f79535-47bb-0310-9956-ffa450edef68
Field not accessed outside its class

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/proxy/trunk@1582299 13f79535-47bb-0310-9956-ffa450edef68