Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56406
Correct typo in example in VirtualDirContext javadoc.

Other documentation files (config/context.xml, config/resources.xml) are OK.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1586972 13f79535-47bb-0310-9956-ffa450edef68