Maintenance: Bump rubocop from 1.25.1 to 1.26.0

Bumps [rubocop](https://github.com/rubocop/rubocop) from 1.25.1 to 1.26.0.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop/rubocop/compare/v1.25.1...v1.26.0)

Gemfile.lock

@@ -458,13 +458,13 @@ GEM
       rspec-support (~> 3.10)
     rspec-support (3.11.0)
     rszr (0.5.2)
-    rubocop (1.25.1)
+    rubocop (1.26.0)
       parallel (~> 1.10)
       parser (>= 3.1.0.0)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
       rexml
-      rubocop-ast (>= 1.15.1, < 2.0)
+      rubocop-ast (>= 1.16.0, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
     rubocop-ast (1.16.0)