Support newer JRubies

[olleolleolle]

This PR adds support for recognising ~three~ ~five~ many new releases of JRuby.

❌: yet to be added to this PR.

💚: added to this PR.

👍: already supported.

Done?	JRuby version	RUBY_VERSION
❌	9.1.1.0	2.3.0
👍	9.1.2.0	2.3.0
❌	9.1.3.0	2.3.1
❌	9.1.4.0	2.3.1
❌	9.1.5.0	2.3.1
❌	9.1.6.0	2.3.1
💚	9.1.7.0	2.3.1
💚	9.1.8.0	2.3.1
❌	9.1.9.0	2.3.3
💚	9.1.10.0	2.3.3
❌	9.1.11.0	2.3.3
💚	9.1.12.0	2.3.3
💚	9.1.13.0	2.3.3
💚	9.1.14.0	2.3.3
💚	9.1.15.0	2.3.3
💚	9.1.16.0	2.3.3
💚	9.1.17.0	2.3.3
💚	9.2.0.0	2.5.0

Source: Full list of JRuby releases

Questions for reviewer:

• Did I understand the "pessimistic version" specs correctly?

See #34

(To make builds go, I had to do the same fix as #33 in this PR: require 'tmpdir')

[olleolleolle]

I updated the list with 9.1.14.0-9.2.0.0.