The Ruby compilation configuration in the .gemspec file is modified to be compatible with later bundler versions.

If use the version laster to build the ruby lib will fail by a error like this:

/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb10: warning: constant Gem::ConfigMap is deprecated.

Want to be compatible with the new bundler version.

From the content in the link, there is no problem.
semver