JRuby reflective access & deprecation warnings

[nickcharlton]

On CI (example build), we're getting the following set of deprecation warnings on JRuby:

WARNING: An illegal reflective access operation has occurred
874WARNING: Illegal reflective access by org.jruby.ext.openssl.SecurityHelper (file:/home/travis/.rvm/rubies/jruby-head/lib/ruby/stdlib/jopenssl.jar) to constructor java.security.cert.CertificateFactory(java.security.cert.CertificateFactorySpi,java.security.Provider,java.lang.String)
875WARNING: Please consider reporting this to the maintainers of org.jruby.ext.openssl.SecurityHelper
876WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
877WARNING: All illegal access operations will be denied in a future release
878[DEPRECATED] The --binstubs option will be removed in favor of `bundle binstubs`