I attempted installing gherkin-2.12.2 without having ruby-beautify installed. It failed trying to execute rbeautify. After installing ruby-beautify, gherkin passed that step so it seems clear that there is a dependency on ruby-beautify missing at least for build time.
Now fixed, thanks for the report.
*** Bug 553480 has been marked as a duplicate of this bug. ***
*** Bug 553910 has been marked as a duplicate of this bug. ***
It looks like the dependency did not get added, possibly when the keywords were dropped. It should now be there.