Fix reference to static fields through instance

START_TAG and END_DOCUMENT are static fields and should be
accessed in a static way as per notes in the official documentation
at http://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html

Change-Id: I6a626f9efe33605d08ea136eca7be8fc9a7e402d
Signed-off-by: Manuel R. Ciosici <manuelrciosici@gmail.com>