JRuby to support \K escape sequence in 9.1.15.0

Allow me to celebrate the JRuby team (and nearby efforts) in that the next patch release of it will include \K as a regular expression special character. This GitHub Issue was just closed with a resolution in the Joni library: https://github.com/jruby/jruby/issues/4871 Its support is in a little select company, randomly listed at StackOverflow, which has …