Screenruler doesn't start (Lubuntu 18.04.2)

The console output:

user@user:~$ screenruler
Loading libraries...
/usr/share/screenruler/utils/addons_ruby.rb:42: warning: constant ::Fixnum is deprecated
Traceback (most recent call last):
 35: from /usr/bin/screenruler:51:in `<main>'
 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.rb:11: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/gtk2/base.rb:12: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/glib2.rb:127: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:46:in `compatible?'
  5: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:12:in `bundler_version'
  4: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:29:in `bundler_version_with_reason'
  3: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:81:in `lockfile_version'
  2: from /usr/lib/ruby/2.5.0/rubygems/bundler_version_finder.rb:93: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)
user@user:~$

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: screenruler 0.960+bzr41-1.2
ProcVersionSignature: Ubuntu 4.15.0-54.58-generic 4.15.18
Uname: Linux 4.15.0-54-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.6
Architecture: amd64
CurrentDesktop: LXDE
Date: Wed Jul 10 01:06:06 2019
EcryptfsInUse: Yes
InstallationDate: Installed on 2018-06-11 (393 days ago)
InstallationMedia: Lubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
SourcePackage: screenruler
UpgradeStatus: No upgrade log present (probably fresh install)