CI: Introduce ruby.{2,3,5}, spell check and disallow errors of bundler:audit
For now, we don't test against ruby 2.1, because rails-observers-0.1.5 requires ruby version >= 2.2.2.
Relates #84 (closed)
For now, we don't test against ruby 2.1, because rails-observers-0.1.5 requires ruby version >= 2.2.2.
Relates #84 (closed)