Update rubocop requirement to ~> 0.54.0 (#72)

Updates the requirements on [rubocop](https://github.com/bbatsov/rubocop) to permit the latest version.
- [Release notes](https://github.com/bbatsov/rubocop/releases)
- [Changelog](https://github.com/bbatsov/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v0.53.0...v0.54.0)

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

Gemfile.lock

@@ -81,7 +81,7 @@ GEM
     method_source (0.9.0)
     minitest (5.11.3)
     parallel (1.12.1)
-    parser (2.5.0.3)
+    parser (2.5.0.4)
       ast (~> 2.4.0)
     powerpack (0.1.1)
     pry (0.11.3)
@@ -111,7 +111,7 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.7.0)
     rspec-support (3.7.1)
-    rubocop (0.53.0)
+    rubocop (0.54.0)
       parallel (~> 1.10)
       parser (>= 2.5)
       powerpack (~> 0.1)
@@ -150,7 +150,7 @@ DEPENDENCIES
   hets-agent!
   rake (~> 12.3.0)
   rspec (~> 3.7.0)
-  rubocop (~> 0.53.0)
+  rubocop (~> 0.54.0)
 
 BUNDLED WITH
    1.16.1

hets-agent.gemspec

@@ -34,7 +34,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rspec', '~> 3.7.0'
 
   spec.add_development_dependency 'codecov', '~> 0.1.10'
-  spec.add_development_dependency 'rubocop', '~> 0.53.0'
+  spec.add_development_dependency 'rubocop', '~> 0.54.0'
 
   # We want to have these in the production environment as well in case we need
   # to debug the application: