Run tests with the latest and currently supported Rubies in Travis CI
Ruby 2.3 is end-of-life (EOL) officially, however, macOS still uses this in default.
Some users run Terraforming with system Ruby (without installing the latest Ruby or using rbenv), so Terraforming should also support macOS' default Ruby.
Coverage remained the same at 100.0% when pulling 849e480b4bccdfd610f3a591177b2410e3c626a2 on dtan4/use-latest-ruby-1904 into 1b5585f35c4d9b6503801ff80b4f2eb199c9c18c on master.
WHAT
Run tests with the latest and currently supported Rubies in Travis CI
Ruby 2.3 is end-of-life (EOL) officially, however, macOS still uses this in default. Some users run Terraforming with system Ruby (without installing the latest Ruby or using rbenv), so Terraforming should also support macOS' default Ruby.
WHY
The tool should support the latest Ruby in its lifetime. Additionally, it doesn't have to support the old Rubies once they became end-of-life (EOL).
REF
Ruby Maintenance Branches