Bump rubocop-rspec from 2.5.0 to 2.6.0

Bumps [rubocop-rspec](https://github.com/rubocop/rubocop-rspec) from 2.5.0 to 2.6.0.
- [Release notes](https://github.com/rubocop/rubocop-rspec/releases)
- [Changelog](https://github.com/rubocop/rubocop-rspec/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop/rubocop-rspec/compare/v2.5.0...v2.6.0)

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

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

Gemfile.lock

@@ -430,7 +430,7 @@ GEM
       rubocop-ast (>= 1.12.0, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.12.0)
+    rubocop-ast (1.13.0)
       parser (>= 3.0.1.1)
     rubocop-performance (1.12.0)
       rubocop (>= 1.7.0, < 2.0)
@@ -439,7 +439,7 @@ GEM
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.7.0, < 2.0)
-    rubocop-rspec (2.5.0)
+    rubocop-rspec (2.6.0)
       rubocop (~> 1.19)
     ruby-progressbar (1.11.0)
     ruby-vips (2.1.3)