Rely soley on rubocop-lts for linting

.rubocop.yml

-inherit_from: .rubocop_todo.yml
-
 inherit_gem:
-  rubocop-lts: rubocop-lts.yml
-
-Metrics/BlockLength:
-  ExcludedMethods:
-    - context
-    - describe
-    - it
-    - shared_context
-    - shared_examples
-    - shared_examples_for
-    - namespace
-    - draw
+  rubocop-lts: config/rubygem_rspec.yml

version_gem.gemspec

@@ -2,64 +2,59 @@
 
 # Get the GEMFILE_VERSION without *require* "my_gem/version", for code coverage accuracy
 # See: https://github.com/simplecov-ruby/simplecov/issues/557#issuecomment-825171399
-load 'lib/version_gem/version.rb'
+load "lib/version_gem/version.rb"
 gem_version = VersionGem::Version::VERSION
 VersionGem::Version.send(:remove_const, :VERSION)
 
 Gem::Specification.new do |spec|
-  spec.cert_chain  = ['certs/pboling.pem']
-  spec.signing_key = File.expand_path('~/.ssh/gem-private_key.pem') if $PROGRAM_NAME =~ /gem\z/
+  spec.cert_chain = ["certs/pboling.pem"]
+  spec.signing_key = File.expand_path("~/.ssh/gem-private_key.pem") if $PROGRAM_NAME.end_with?("gem")
 
-  spec.name = 'version_gem'
+  spec.name = "version_gem"
   spec.version = gem_version
-  spec.authors = ['Peter Boling']
-  spec.email = ['peter.boling@gmail.com', 'oauth-ruby@googlegroups.com']
-
-  spec.summary = 'Enhance your VERSION! Sugar for Version modules.'
-  spec.description = 'Versions are good. Versions are cool. Versions will win.'
-  spec.homepage = 'https://gitlab.com/oauth-xx/version_gem'
-  spec.license = 'MIT'
-  spec.required_ruby_version = '>= 2.2'
-
-  spec.metadata['homepage_uri'] = spec.homepage
-  spec.metadata['source_code_uri'] = "#{spec.homepage}/-/tree/v#{spec.version}"
-  spec.metadata['changelog_uri'] = "#{spec.homepage}/-/blob/v#{spec.version}/CHANGELOG.md"
-  spec.metadata['bug_tracker_uri'] = "#{spec.homepage}/-/issues"
-  spec.metadata['documentation_uri'] = "https://www.rubydoc.info/gems/#{spec.name}/#{spec.version}"
-  spec.metadata['wiki_uri'] = "#{spec.homepage}/-/wiki"
-  spec.metadata['mailing_list_uri'] = 'https://groups.google.com/g/oauth-ruby'
-  spec.metadata['funding_uri'] = 'https://liberapay.com/pboling'
-  spec.metadata['rubygems_mfa_required'] = 'true'
+  spec.authors = ["Peter Boling"]
+  spec.email = ["peter.boling@gmail.com", "oauth-ruby@googlegroups.com"]
+
+  spec.summary = "Enhance your VERSION! Sugar for Version modules."
+  spec.description = "Versions are good. Versions are cool. Versions will win."
+  spec.homepage = "https://gitlab.com/oauth-xx/version_gem"
+  spec.license = "MIT"
+  spec.required_ruby_version = ">= 2.2"
+
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = "#{spec.homepage}/-/tree/v#{spec.version}"
+  spec.metadata["changelog_uri"] = "#{spec.homepage}/-/blob/v#{spec.version}/CHANGELOG.md"
+  spec.metadata["bug_tracker_uri"] = "#{spec.homepage}/-/issues"
+  spec.metadata["documentation_uri"] = "https://www.rubydoc.info/gems/#{spec.name}/#{spec.version}"
+  spec.metadata["wiki_uri"] = "#{spec.homepage}/-/wiki"
+  spec.metadata["mailing_list_uri"] = "https://groups.google.com/g/oauth-ruby"
+  spec.metadata["funding_uri"] = "https://liberapay.com/pboling"
+  spec.metadata["rubygems_mfa_required"] = "true"
 
   spec.files = Dir[
-    'lib/**/*',
-    'CHANGELOG.md',
-    'CODE_OF_CONDUCT.md',
-    'CONTRIBUTING.md',
-    'LICENSE.txt',
-    'README.md',
-    'SECURITY.md',
+    "lib/**/*",
+    "CHANGELOG.md",
+    "CODE_OF_CONDUCT.md",
+    "CONTRIBUTING.md",
+    "LICENSE.txt",
+    "README.md",
+    "SECURITY.md",
   ]
-  spec.require_paths = ['lib']
+  spec.require_paths = ["lib"]
 
   # Tests
-  spec.add_development_dependency 'rspec'
-  spec.add_development_dependency 'rspec-block_is_expected'
+  spec.add_development_dependency("rspec", "~> 3.12")
+  spec.add_development_dependency("rspec-block_is_expected", "~> 1.0")
 
   # Development Tasks
-  spec.add_development_dependency 'rake'
+  spec.add_development_dependency("rake", "~> 13.0")
 
-  # Debugger
-  spec.add_development_dependency 'pry'
+  # Dev Console
+  spec.add_development_dependency("pry")
 
   # Linting - rubocop-lts v8 is a rubocop wrapper for Ruby >= 2.2,
   #   and should only be bumped when dropping old Ruby support
-  # see: https://dev.to/pboling/rubocop-lts-1e31
-  spec.add_development_dependency 'rubocop-lts', ['~> 8.0', '>= 8.0.2']
-
-  # Lint RSpec code
-  spec.add_development_dependency 'rubocop-rspec'
-
-  # Add performance linting
-  spec.add_development_dependency 'rubocop-performance'
+  # NOTE: it can only be installed on, and run on Ruby >= 2.7, so we add the dependency in the Gemfile.
+  # see: https://rubocop-lts.gitlab.io
+  # spec.add_development_dependency 'rubocop-lts', ['~> 8.1', '>= 8.1.1']
 end