update notes for 9.1
duplicate slipped in
interfaces no longer have a new
more JI release notes
notes on improved arities with become_java!
notes on changed to_ary
removed java.lang.Throwable#to_str
notes on Java array equality
add Map proxy changes
note on pkg.to_s behavior change
mention changes after merging #3754
Updated JRuby 9.1.0.0 Release Notes (markdown)
notes on stack-trace filtering
9.1 changelog tracking release page