Drop support for RuboCop 0.81 or lower

Follow up to rubocop/rubocop-performance#111.

This PR prepares to use RuboCop's new development API.

Author: koic

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Changes
+
+* [#82](https://github.com/rubocop-hq/rubocop-minitest/pull/82): Drop support for RuboCop 0.81 or lower. ([@koic][])
+
 ## 0.9.0 (2020-04-13)
 
 ### Bug fixes

rubocop-minitest.gemspec

@@ -34,6 +34,6 @@ Gem::Specification.new do |spec|
   spec.executables = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
-  spec.add_runtime_dependency 'rubocop', '>= 0.74'
+  spec.add_runtime_dependency 'rubocop', '>= 0.82'
   spec.add_development_dependency 'minitest', '~> 5.11'
 end