Ruby 2.3.0 and frozen_string_literal magic comment

[tmaier]

• Adds ruby 2.3.0 for Travis CI tests
• Updates all ruby versions specified for Travis CI tests to be in-line with versions supported by Heroku
• Add # frozen_string_literal: true to all ruby files to freeze all strings

FAQ

Did you actually test/measure any performance improvement by this change?

Nope.

Did you run the tests?

$ bundle exec rake was successful.

Did you add the magic comments manually?

No, I used https://github.com/Invoca/magic_frozen_string_literal

[tmaier]

Alright, the build fails on Ruby 1.9.3. This seems to be related to rubygems/bundler#3559.

Two options:

1. Install the latest bundler version on travis as a workaround
2. drop support for Ruby 1.9.3. This ruby version is anyway not maintained anymore.

Which one do you prefer?

[tmaier]

Issue with Ruby 1.9.3 seems to be resolved when using Travis CIs container based infrastructure.

[geemus]

Thanks!