Travis: RVM note, extract env, cache bundler right; Appveyor: fix build

[olleolleolle]

This tiny change fixes ~three~ five things:

Travis

• speed: RVM does gem update --system on its own
• readability: configure JRUBY_OPTS as env global
• clarity: Travis YAML config cache shorthand for bundler corrected
• update: use latest JRuby in CI matrix - jruby-9.1.14.0

Appveyor

• Build fix: used https://www.appveyor.com/docs/lang/ruby/ as a template and harmonized our configuration to that, and the tests began passing.

[olleolleolle]

@sickill If this runs green, I'll merge it.