Bump rubocop-rails from 2.7.1 to 2.8.0 (#413)

Bumps [rubocop-rails](https://github.com/rubocop-hq/rubocop-rails) from 2.7.1 to 2.8.0.
- [Release notes](https://github.com/rubocop-hq/rubocop-rails/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop-rails/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-rails@v2.7.1...v2.8.0)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

Gemfile.lock

@@ -226,7 +226,7 @@ GEM
     mini_portile2 (2.4.0)
     mini_racer (0.3.1)
       libv8 (~> 8.4.255)
-    minitest (5.14.1)
+    minitest (5.14.2)
     msgpack (1.3.3)
     nenv (0.3.0)
     net-scp (3.0.0)
@@ -340,7 +340,7 @@ GEM
       unicode-display_width (>= 1.4.0, < 2.0)
     rubocop-ast (0.3.0)
       parser (>= 2.7.1.4)
-    rubocop-rails (2.7.1)
+    rubocop-rails (2.8.0)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 0.87.0)