OSX and image not found readline.bundle

Something changed recently in my osx configuration, I'm not sure what, but it broke readline on the macbook.

The key part of the error message  was:

Library not loaded: /usr/local/opt/readline/lib/libreadline.7.dylib (LoadError)
  Referenced from: /Users/stokern/.rbenv/versions/2.5.3/lib/ruby/2.5.0/x86_64-darwin17/readline.bundle
  Reason: image not found - /Users/stokern/.rbenv/versions/2.5.3/lib/ruby/2.5.0/x86_64-darwin17/readline.bundle


The fix was to add the ruby readline gem:

group :development, :test do

  ...

  gem 'rb-readline'

end

This is the second time this has caught me out, so I thought I'd document it.

You're welcome