Homebrew must be run under Ruby 2.3! You're running 2.0.0. (RuntimeError)

.env
/macOS Sierra 10.12.6
/ruby 2.0.0p648

わざわざ残すまでもないことだけれど、一応メモ。

brew install package_name

で、表題エラー

Homebrew must be run under Ruby 2.3! You're running 2.0.0. (RuntimeError)

Homebrewを長らくupdateしていなかったので、update

brew update

Link:
https://github.com/travis-ci/travis-ci/issues/8552#issuecomment-335430374