$ jruby -S rails s puma
TypeError: no implicit conversion of Regexp into String
   join at org/jruby/RubyArray.java:1760
  <top> at /Users/z/bin/spring:11
   load at org/jruby/RubyKernel.java:955
  <top> at /Users/z/bin/rails:3
$ rvm list

rvm rubies

   jruby-9.0.5.0 [ x86_64 ]
=* jruby-9.1.7.0 [ x86_64 ]
   ruby-2.2.3 [ x86_64 ]
   ruby-2.3.0 [ x86_64 ]
   ruby-2.3.1 [ x86_64 ]

# => - current
# =* - current && default
#  * - default

$ jruby -v
jruby 9.1.7.0 (2.3.1) 2017-01-11 68056ae Java HotSpot(TM) 64-Bit Server VM 25.141-b15 on 1.8.0_141-b15 +jit [darwin-x86_64]

ruby '2.3.1', engine: 'jruby', engine_version: '9.1.7.0'