crash on start

When attempting to run screenruler on ubuntu 19.04, one got:

$ screenruler
Loading libraries...
/usr/share/screenruler/utils/addons_ruby.rb:42: warning: constant ::Fixnum is deprecated
Traceback (most recent call last):
 41: from /usr/bin/screenruler:51:in `<main>'
 40: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `require'
 39: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `each'
 38: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `block in require'
 37: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 36: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 35: from /usr/lib/ruby/vendor_ruby/gtk2.rb:11:in `<top (required)>'
 34: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `require'
 33: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `each'
 32: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `block in require'
 31: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 30: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 29: from /usr/lib/ruby/vendor_ruby/gtk2/base.rb:14:in `<top (required)>'
 28: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `require'
 27: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `each'
 26: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `block in require'
 25: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 24: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 23: from /usr/lib/ruby/vendor_ruby/pango.rb:18:in `<top (required)>'
 22: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `require'
 21: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `each'
 20: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `block in require'
 19: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 18: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
 17: from /usr/lib/ruby/vendor_ruby/cairo.rb:52:in `<top (required)>'
 16: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `require'
 15: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `each'
 14: from /usr/share/screenruler/utils/addons_ruby.rb:59:in `block in require'
 13: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:39:in `require'
 12: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:128:in `rescue in require'
 11: from /usr/lib/ruby/2.5.0/rubygems.rb:213:in `try_activate'
 10: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1063:in `find_by_path'
  9: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1063:in `find'
  8: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1063:in `each'
  7: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1064:in `block in find_by_path'
  6: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:36:in `compatible?'
  5: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:4:in `bundler_version'
  4: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:19:in `bundler_version_with_reason'
  3: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:65:in `lockfile_version'
  2: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:77:in `lockfile_contents'
  1: from /usr/lib/ruby/2.5.0/rubygems/util.rb:116:in `traverse_parents'
/usr/share/screenruler/utils/addons_ruby.rb:62:in `loop': wrong number of arguments (given 0, expected 2..3) (ArgumentError)

no window is shown and no app is running