Use just OpenJDK in Travis CI
Use just OpenJDK in Travis CI

Replace OracleJDK with OpenJDK, the former is no longer included by
default in newer dists (Xenial).

Signed-off-by: thc202 <43af82ef30812a20fbcf38b99a6f72cdd3a89ac1@gmail.com>

kingthorin/zap-extensions,zapbot/zap-extensions,zaproxy/zap-extensions,zapbot/zap-extensions,psiinon/zap-extensions,secdec/zap-extensions,psiinon/zap-extensions,kingthorin/zap-extensions,zaproxy/zap-extensions,psiinon/zap-extensions,secdec/zap-extensions,kingthorin/zap-extensions,psiinon/zap-extensions,denniskniep/zap-extensions,veggiespam/zap-extensions,secdec/zap-extensions,zapbot/zap-extensions,zaproxy/zap-extensions,secdec/zap-extensions,veggiespam/zap-extensions,kingthorin/zap-extensions,thc202/zap-extensions,veggiespam/zap-extensions,kingthorin/zap-extensions,denniskniep/zap-extensions,zaproxy/zap-extensions,kingthorin/zap-extensions,denniskniep/zap-extensions,zapbot/zap-extensions,thc202/zap-extensions,thc202/zap-extensions,thc202/zap-extensions,denniskniep/zap-extensions,secdec/zap-extensions,veggiespam/zap-extensions,zapbot/zap-extensions,veggiespam/zap-extensions,denniskniep/zap-extensions,psiinon/zap-extensions,secdec/zap-extensions,denniskniep/zap-extensions,psiinon/zap-extensions,zapbot/zap-extensions,thc202/zap-extensions,secdec/zap-extensions,thc202/zap-extensions,zaproxy/zap-extensions,zaproxy/zap-extensions,veggiespam/zap-extensions