fix: drop Rails dependency (#73)

Author: route

.gitignore

@@ -4,3 +4,4 @@ spec/dummy/log
 spec/dummy/db/**.sqlite3
 spec/dummy/tmp/storage/**/*
 /coverage/
+.bundle

active_storage_base64.gemspec

@@ -15,9 +15,11 @@ Gem::Specification.new do |s|
   s.required_ruby_version = '>= 2.7.0'
 
   # Dependencies
-  s.add_dependency 'rails', '>= 7.0'
+  s.add_dependency 'activestorage', '>= 7.0'
+  s.add_dependency 'activesupport', '>= 7.0'
 
   # Development dependencies
+  s.add_development_dependency 'rails', '>= 7.0'
   s.add_development_dependency 'pry-rails', '~> 0.3.6'
   s.add_development_dependency 'reek', '~> 6.0.6'
   s.add_development_dependency 'rspec-rails', '~> 3.8.0'