Add rubocop for dev

Gemfile

@@ -6,4 +6,5 @@ group :development do
   gem 'rake'
   gem 'sqlite3', '~> 1.6.0'
   gem 'test-unit'
+  gem 'rubocop'
 end

Gemfile.lock

@@ -23,6 +23,7 @@ GEM
       minitest (>= 5.1)
       mutex_m
       tzinfo (~> 2.0)
+    ast (2.4.2)
     base64 (0.2.0)
     bigdecimal (3.1.8)
     coderay (1.1.3)
@@ -31,22 +32,49 @@ GEM
     drb (2.2.1)
     i18n (1.14.5)
       concurrent-ruby (~> 1.0)
+    json (2.7.2)
+    language_server-protocol (3.17.0.3)
     method_source (1.0.0)
     mini_portile2 (2.8.1)
     minitest (5.24.1)
     mutex_m (0.2.0)
+    parallel (1.25.1)
+    parser (3.3.4.0)
+      ast (~> 2.4.1)
+      racc
     power_assert (2.0.3)
     pry (0.14.2)
       coderay (~> 1.1)
       method_source (~> 1.0)
+    racc (1.8.0)
+    rainbow (3.1.1)
     rake (13.0.6)
+    regexp_parser (2.9.2)
+    rexml (3.3.1)
+      strscan
+    rubocop (1.65.0)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 2.4, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.31.3)
+      parser (>= 3.3.1.0)
+    ruby-progressbar (1.13.0)
     sqlite3 (1.6.0)
       mini_portile2 (~> 2.8.0)
+    strscan (3.1.0)
     test-unit (3.5.7)
       power_assert
     timeout (0.4.1)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
+    unicode-display_width (2.5.0)
 
 PLATFORMS
   ruby
@@ -55,6 +83,7 @@ DEPENDENCIES
   acts_as_commentable!
   pry
   rake
+  rubocop
   sqlite3 (~> 1.6.0)
   test-unit