Maven artifacts changed

[Gordon Pettey]

For POI 3.12, the Maven artifact classifier for javadoc got an "s" added,
so is now -javadocs.jar. This is non-standard and breaks tools that
auto-download a javadoc classifier along with the main artifact. The POI
3.13 snapshots have the same problem. Looked through SVN history, and
1637827 may be relevant, search for added "javadocs-${DSTAMP}".