Bump rubocop-performance from 1.8.0 to 1.8.1

Bumps [rubocop-performance](https://github.com/rubocop-hq/rubocop-performance) from 1.8.0 to 1.8.1.
- [Release notes](https://github.com/rubocop-hq/rubocop-performance/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop-performance/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-performance@v1.8.0...v1.8.1)

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

Gemfile.lock

@@ -230,8 +230,9 @@ GEM
       unicode-display_width (>= 1.4.0, < 2.0)
     rubocop-ast (0.5.0)
       parser (>= 2.7.1.5)
-    rubocop-performance (1.8.0)
+    rubocop-performance (1.8.1)
       rubocop (>= 0.87.0)
+      rubocop-ast (>= 0.4.0)
     rubocop-rails (2.8.1)
       activesupport (>= 4.2.0)
       rack (>= 1.1)