upgrade to Javassist 3.18.1-GA

Wildfly 8, EAP 6.2, Hibernate ORM 4.2+, etc. have all upgraded to Javassist 3.18.1. 3.16 introduced a new Proxy interface (the old ProxyObject extends it). Various containers cause ClassCastExceptions if the weld-osgi-bundle (and its older Javassist dependency) are on the classpath.

See https://hibernate.atlassian.net/browse/HHH-8778 for a related discussion. JASSIST-144 is the fix that introduced the new interface.