Strange error propably related with ruby gem version

After type `ls` this output display:

```
Traceback (most recent call last):
2: from /usr/bin/colorls:23:in `'
1: from /usr/lib/ruby/2.7.0/rubygems.rb:294:in `activate_bin_path'
/usr/lib/ruby/2.7.0/rubygems.rb:275:in `find_spec_for_exe': can't find gem colorls (>= 0.a) with executable colorls (Gem::GemNotFoundException)
```

Reproduce the failure with `ls`, then inspect `/usr/bin/colorls` and the RubyGems paths shown in the traceback. Verify how the colorls gem and its `colorls` executable are installed and resolved; done means `ls` launches colorls without `Gem::GemNotFoundException`.

Written by the indexing model from the issue text.