Fix grammar in message.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1543240 13f79535-47bb-0310-9956-ffa450edef68
Statement unnecessarily nested within else clause.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1543241 13f79535-47bb-0310-9956-ffa450edef68