Updating from Jetty 9.3.6 to current 9.3.15?

[Rich Graves]

Lame question here. While upgrading from IdP 3.2.1 to 3.3 I figure I
should get up to date on Jetty as well (hasn't been a priority because
we're behind Apache anyway). Anything past Jetty 9.3.6 seems to fail
with:

Error: Could not find or load main class org.eclipse.jetty.xml.XmlConfiguration

I am running my test instances with

sh -c '(cd ~/shibboleth-idp/jetty-base && java -jar
/opt/jetty/start.jar
jetty.home=/opt/jetty-distribution-9.3.6.v20151106 jetty.base=.)'

/opt/jetty-distribution-* are unmodified from download.

lib/jetty-xml-VERSION.jar exists containing the indicated class. What
documentation or obvious thing am I missing?

Is Jetty 9.4.0 supported/recommended? 9.3 doesn't seem in danger of EOL.