[CONFIGURATION-663] Fixed a typo in the upgrade guide.
[CONFIGURATION-663] Fixed a typo in the upgrade guide.

Thanks to kap4020 at gmail dot com for spotting this.

git-svn-id: 0d31da9e303333003508381311333cf78a25d41b@1792079 13f79535-47bb-0310-9956-ffa450edef68

apache/commons-configuration,apache/commons-configuration,apache/commons-configuration