Update rubocop requirement from ~> 1.65.0 to ~> 1.66.0 (#229)

* Update rubocop requirement from ~> 1.65.0 to ~> 1.66.0

Updates the requirements on [rubocop](https://github.com/rubocop/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v1.65.0...v1.66.0)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

* Fix lint

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: なつき <i@ntk.me>

Gemfile

@@ -7,7 +7,7 @@ gemspec
 group :development do
  gem 'rake', '>= 13'
  gem 'rspec', '~> 3.13.0'
- gem 'rubocop', '~> 1.65.0'
+ gem 'rubocop', '~> 1.66.0'
  gem 'rubocop-performance', '~> 1.21.0'
  gem 'rubocop-rake', '~> 0.6.0'
  gem 'rubocop-rspec', '~> 3.0.1'

lib/sass/value/number.rb

@@ -290,7 +290,7 @@ def coerce_or_convert_value(new_numerator_units, new_denominator_units,
 
  compatibility_error = lambda {
  unless other.nil?
- message = +"#{self} and"
+ message = "#{self} and"
  message << " $#{other_name}:" unless other_name.nil?
  message << " #{other} have incompatible units"
  message << " (one has units and the other doesn't)" if unitless? || other_unitless