Eliminate use of deprecated methods from JRuby

[headius]

There are uses of many methods that have been deprecated in JRuby, some for years and some recently. We should audit these deprecations and try to safely move to the replacement options.

Known issues:

• RubyString.cat19, deprecated in JRuby 9.4.7.0 and replaced with catWithCodeRange. Probably update after JRuby 10 is released because many users are still on earlier JRuby versions. See Merge 1.1 into master (redux - with all specs passing + bumped dependency minor versions) #262 (comment).