Fix dependency resolution of Javassist

Reflections uses the old group-id 'javassist', but Play references a
newer version with the current group-id 'org.javassist'. This leads
to a dependency resolution problem when doing an assembly:

[error] (*:assembly) deduplicate: different file contents found in the following:
[error] /home/rtyley/.ivy2/cache/javassist/javassist/jars/javassist-3.12.1.GA.jar:javassist/bytecode/stackmap/Tracer.class
[error] /home/rtyley/.ivy2/cache/org.javassist/javassist/jars/javassist-3.16.1-GA.jar:javassist/bytecode/stackmap/Tracer.class

http://code.google.com/p/reflections/issues/detail?id=140