Some troubles on installing `rainbow` on old `rake` (#108)
Some troubles on installing `rainbow` on old `rake` (#108)

Error looks like:
```
Installing parallel_tests 2.12.0
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /usr/local/bundle/gems/rainbow-2.2.1/ext
/usr/local/bin/ruby mkrf_conf.rb

current directory: /usr/local/bundle/gems/rainbow-2.2.1/ext
rake RUBYARCHDIR=/usr/local/bundle/extensions/x86_64-linux/2.3.0/rainbow-2.2.1 RUBYLIBDIR=/usr/local/bundle/extensions/x86_64-linux/2.3.0/rainbow-2.2.1
/usr/local/lib/ruby/site_ruby/2.3.0/rubygems.rb:270:in `find_spec_for_exe': can't find gem rake (>= 0.a) (Gem::GemNotFoundException)
        from /usr/local/lib/ruby/site_ruby/2.3.0/rubygems.rb:258:in `bin_path'
        from /usr/local/bin/rake:22:in `<main>'

rake failed, exit code 1

Gem files will remain installed in /usr/local/bundle/gems/rainbow-2.2.1 for inspection.
Results logged to /usr/local/bundle/extensions/x86_64-linux/2.3.0/rainbow-2.2.1/gem_make.out

An error occurred while installing rainbow (2.2.1), and Bundler cannot continue.
Make sure that `gem install rainbow -v '2.2.1'` succeeds before bundling.
```
ONLYOFFICE/doc-builder-testing,ONLYOFFICE/doc-builder-testing,ONLYOFFICE/doc-builder-testing