Fix appraisal gemfiles to use simple format

Simplify Rails 5.1, 5.2, and 6.0 gemfiles to only include Rails version,
sqlite3 constraint, and gemspec reference, removing unnecessary group
definitions that were causing bundle install conflicts.

Also exclude gemfiles directory from Rubocop checks since these are
auto-generated files.

Author: sudoremo

.rubocop.yml

@@ -5,6 +5,7 @@ AllCops:
     - 'vendor/**/*'
     - 'tmp/**/*'
     - 'inquery.gemspec'
+    - 'gemfiles/**/*'
   SuggestExtensions: false
 
   DisplayCopNames: true

gemfiles/rails_5.1.gemfile

@@ -1,23 +1,8 @@
 # This file was generated by Appraisal
 
-source "https://rubygems.org"
+source 'https://rubygems.org'
 
-gem "rails", "~> 5.1.7"
-gem "sqlite3", "~> 1.3.13"
+gem 'rails', '~> 5.1.7'
+gem 'sqlite3', '~> 1.3.13'
 
-group :development do
-  gem "appraisal"
-  gem "rake"
-end
-
-group :test do
-  gem "minitest"
-  gem "simplecov"
-  gem "sqlite3"
-end
-
-group :lint do
-  gem "rubocop", "~> 1.60"
-end
-
-gemspec path: "../"
+gemspec path: '../'

gemfiles/rails_5.2.gemfile

@@ -1,23 +1,8 @@
 # This file was generated by Appraisal
 
-source "https://rubygems.org"
+source 'https://rubygems.org'
 
-gem "rails", "~> 5.2.6"
-gem "sqlite3", "~> 1.3.13"
+gem 'rails', '~> 5.2.6'
+gem 'sqlite3', '~> 1.3.13'
 
-group :development do
-  gem "appraisal"
-  gem "rake"
-end
-
-group :test do
-  gem "minitest"
-  gem "simplecov"
-  gem "sqlite3"
-end
-
-group :lint do
-  gem "rubocop", "~> 1.60"
-end
-
-gemspec path: "../"
+gemspec path: '../'

gemfiles/rails_6.0.gemfile

@@ -1,23 +1,8 @@
 # This file was generated by Appraisal
 
-source "https://rubygems.org"
+source 'https://rubygems.org'
 
-gem "rails", "~> 6.0.4"
-gem "sqlite3", "~> 1.4.0"
+gem 'rails', '~> 6.0.4'
+gem 'sqlite3', '~> 1.4.0'
 
-group :development do
-  gem "appraisal"
-  gem "rake"
-end
-
-group :test do
-  gem "minitest"
-  gem "simplecov"
-  gem "sqlite3"
-end
-
-group :lint do
-  gem "rubocop", "~> 1.60"
-end
-
-gemspec path: "../"
+gemspec path: '../'