add rubocop as dev dependency and run in CI

.rubocop.yml

@@ -0,0 +1,4 @@
+AllCops:
+  DisabledByDefault: true
+  Exclude:
+    - 'bundler/**/*'

CONTRIBUTING.rdoc

@@ -11,7 +11,7 @@ contributors to follow to reduce the time it takes to get changes merged in.
 2. Ensure that your code blends well with ours:
    * No trailing whitespace
    * Match indentation (two spaces)
-   * Match coding style (+if+, +elsif+, +when+ need trailing +then+)
+   * Match coding style (run <tt>rake rubocop</tt>)
 
 3. If any new files are added or existing files removed in a commit or PR, please update the +Manifest.txt+ accordingly.
    This can be done by running <tt>rake update_manifest</tt>

Rakefile

@@ -102,6 +102,15 @@ rescue LoadError
   end
 end
 
+begin
+  gem "rubocop", "~> 0.54.0"
+  require "rubocop/rake_task"
+
+  RuboCop::RakeTask.new
+rescue LoadError
+  task(:rubocop) { abort "Install the rubocop gem (~> 0.54.0) to run a static analysis" }
+end
+
 # --------------------------------------------------------------------
 # Creating a release
 

rubygems-update.gemspec

@@ -39,4 +39,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency(%q<rake>.freeze, ["~> 12.0"])
   s.add_development_dependency(%q<minitest>.freeze, ["~> 5.0"])
   s.add_development_dependency(%q<simplecov>.freeze, ["~> 0"])
+  s.add_development_dependency(%q<rubocop>.freeze, ["~> 0.54.0"])
 end

util/ci

@@ -56,12 +56,16 @@ when %w(before_script)
     if RUBY_VERSION >= "2.5.0" && RUBY_VERSION < "2.6.0"
       run('gem', %w(install bundler -v 1.16.1))
     end
+
+    run('gem', %w(install rubocop -v 0.54.0))
+
     run('gem', %w(list --details))
     run('gem', %w(env))
   else
     with_retries { run('rake', %w(spec:travis:deps)) }
   end
 when %w(script)
+  run('rake rubocop')
   if TOOL.rubygems?
     run('rake test')
   else