Travis build fails with bundler 2.x

[MariuszCwikla]

Travis build fails:

$ gem install bundler
YAML safe loading is not available. Please upgrade psych to a version that supports safe loading (>= 2.0).
Fetching: bundler-2.0.1.gem (100%)
ERROR:  Error installing bundler:
	The last version of bundler (>= 0) to support your Ruby & RubyGems was 1.17.3. Try installing it with `gem install bundler -v 1.17.3`
	bundler requires Ruby version >= 2.3.0. The current ruby version is 1.9.1.
The command "gem install bundler" failed and exited with 1 during .

I already performed some investigation:

• bundler 2.0 is used by travis - https://docs.travis-ci.com/user/languages/ruby/#bundler-20
• but bundler 2.0 is not compatible with ruby <= 2.2 (which is defined in .travis.yml)
• I tried bundler 1.x which fixes ruby 1.9.3, 2.0, 2.1 using instructions from travis team, but jruby build still fails
• fixing jruby build will require some hacking

What do you think should be done (drop support for ruby 2.2 or force to use bundler 1.x)?

I can help on fixing this - I've tested above "hack" to use bundler 1.x and works fine.

After that I have another fix #11