Downgrade to ActiveRecord 6 to retain compatibility with Ruby 2.6

Author: amotl

activerecord-crate-adapter.gemspec

@@ -49,6 +49,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec", "~> 2.14"
 
-  spec.add_dependency('activerecord', '~> 7')
+  spec.add_dependency('activerecord', '~> 6')
   spec.add_dependency('crate_ruby', '~> 0.2')
 end