Maintenance: 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)

Gemfile.lock

@@ -511,7 +511,7 @@ 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-faker (1.1.0)
       faker (>= 2.12.0)
@@ -527,7 +527,7 @@ 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-saml (1.13.0)