[DRE-maint] Bug#893822: ruby-pygments.rb FTBFS with Ruby 2.5

[Adrian Bunk]

Source: ruby-pygments.rb
Version: 1.2.0-1
Severity: serious

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/ruby-pygments.rb.html

...
┌──────────────────────────────────────────────────────────────────────────────┐
│ Run tests for ruby2.5 from debian/ruby-tests.rb                              │
└──────────────────────────────────────────────────────────────────────────────┘

RUBYLIB=/build/1st/ruby-pygments.rb-1.2.0/debian/ruby-pygments.rb/usr/lib/ruby/vendor_ruby:. GEM_PATH=debian/ruby-pygments.rb/usr/share/rubygems-integration/all:/var/lib/gems/2.5.0:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.5.0:/usr/share/rubygems-integration/2.5.0:/usr/share/rubygems-integration/all ruby2.5 debian/ruby-tests.rb
/usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require': cannot load such file -- ubygems (LoadError)
	from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
rake aborted!
Command failed with status (1)

Tasks: TOP => default => test
(See full trace by running task with --trace)
ERROR: Test "ruby2.5" failed. Exiting.
dh_auto_install: dh_ruby --install /build/1st/ruby-pygments.rb-1.2.0/debian/ruby-pygments.rb returned exit code 1
make[1]: *** [debian/rules:18: override_dh_auto_install] Error 1