Bump rubocop-performance from 1.19.1 to 1.21.0

Bumps [rubocop-performance](https://github.com/rubocop/rubocop-performance) from 1.19.1 to 1.21.0.
- [Release notes](https://github.com/rubocop/rubocop-performance/releases)
- [Changelog](https://github.com/rubocop/rubocop-performance/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-performance@v1.19.1...v1.21.0)

---
updated-dependencies:
- dependency-name: rubocop-performance
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -296,9 +296,9 @@ GEM
       unicode-display_width (>= 2.4.0, < 3.0)
     rubocop-ast (1.31.3)
       parser (>= 3.3.1.0)
-    rubocop-performance (1.19.1)
-      rubocop (>= 1.7.0, < 2.0)
-      rubocop-ast (>= 0.4.0)
+    rubocop-performance (1.21.0)
+      rubocop (>= 1.48.1, < 2.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
     rubocop-rails (2.15.2)
       activesupport (>= 4.2.0)
       rack (>= 1.1)