OF-546: Update HSQLDB dependency to match included library.

The HSQLDB library that ships with Openfire (for Ant) is newer than the
dependency that's defined in Maven. This introduces a compatibility issue
at runtime:

> org.jivesoftware.database.SchemaManager - Unexpected token: FILES in statement [ SET FILES]

The difference is likely an oversight, caused by us taking a very long time
to merge the Maven PR. At the time it was created, the dependency was still okay.

xmppserver/pom.xml

@@ -322,9 +322,9 @@
 
         <!-- Database Drivers -->
         <dependency>
-            <groupId>hsqldb</groupId>
+            <groupId>org.hsqldb</groupId>
             <artifactId>hsqldb</artifactId>
-            <version>1.8.0.5</version>
+            <version>2.3.4</version>
         </dependency>
         <dependency>
             <groupId>mysql</groupId>