Update activerecord version to 6

Author: wpolicarpo

VERSION

@@ -1 +1 @@
-5.2.0
+6.0.0.beta1

activerecord-sqlserver-adapter.gemspec

@@ -16,6 +16,6 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ['lib']
-  spec.add_dependency 'activerecord', '~> 5.2.0'
+  spec.add_dependency 'activerecord', '~> 6.0.0.beta3'
   spec.add_dependency 'tiny_tds'
 end