Update rubocop-performance requirement from ~> 1.25.0 to ~> 1.26.0 (#331)

Updates the requirements on [rubocop-performance](https://github.com/rubocop/rubocop-performance) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-performance/releases)
- [Changelog](https://github.com/rubocop/rubocop-performance/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-performance@v1.25.0...v1.26.0)

---
updated-dependencies:
- dependency-name: rubocop-performance
  dependency-version: 1.26.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Gemfile

@@ -8,7 +8,7 @@ group :development do
   gem 'rake', '>= 13'
   gem 'rspec', '~> 3.13.0'
   gem 'rubocop', '~> 1.80.0'
-  gem 'rubocop-performance', '~> 1.25.0'
+  gem 'rubocop-performance', '~> 1.26.0'
   gem 'rubocop-rake', '~> 0.7.1'
   gem 'rubocop-rspec', '~> 3.7.0'
 end