Bump rubocop-rspec from 2.4.0 to 2.8.0 in /dependencies (#2407)

Bumps [rubocop-rspec](https://github.com/rubocop/rubocop-rspec) from 2.4.0 to 2.8.0.
- [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/v2.4.0...v2.8.0)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

dependencies/Gemfile

@@ -8,4 +8,4 @@ gem "rubocop", "~> 1.25.0"
 gem "rubocop-github", "~> 0.17.0"
 gem "rubocop-performance", "~>1.11.0"
 gem "rubocop-rails", "~> 2.7"
-gem "rubocop-rspec", "~> 2.4.0"
+gem "rubocop-rspec", "~> 2.8.0"

dependencies/Gemfile.lock

@@ -16,7 +16,7 @@ GEM
       ast (~> 2.4.1)
     rack (2.2.3)
     rainbow (3.1.1)
-    regexp_parser (2.2.0)
+    regexp_parser (2.2.1)
     rexml (3.2.5)
     rubocop (1.25.0)
       parallel (~> 1.10)
@@ -27,7 +27,7 @@ GEM
       rubocop-ast (>= 1.15.1, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.15.1)
+    rubocop-ast (1.15.2)
       parser (>= 3.0.1.1)
     rubocop-github (0.17.0)
       rubocop
@@ -40,9 +40,8 @@ GEM
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.7.0, < 2.0)
-    rubocop-rspec (2.4.0)
-      rubocop (~> 1.0)
-      rubocop-ast (>= 1.1.0)
+    rubocop-rspec (2.8.0)
+      rubocop (~> 1.19)
     ruby-progressbar (1.11.0)
     tzinfo (2.0.4)
       concurrent-ruby (~> 1.0)
@@ -56,7 +55,7 @@ DEPENDENCIES
   rubocop-github (~> 0.17.0)
   rubocop-performance (~> 1.11.0)
   rubocop-rails (~> 2.7)
-  rubocop-rspec (~> 2.4.0)
+  rubocop-rspec (~> 2.8.0)
 
 BUNDLED WITH
   2.3.5