Remove ActiveSupport class_attribute detection

[viralpraxis]

Resolves #34

[viralpraxis]

It seems like failures are unrelated to these changes. Should be fixed by pushing rubocop -A and rake generate_cops_documentation to master:

diff --git a/docs/modules/ROOT/pages/cops_threadsafety.adoc b/docs/modules/ROOT/pages/cops_threadsafety.adoc
index c2e613a..e6cba0c 100644
--- a/docs/modules/ROOT/pages/cops_threadsafety.adoc
+++ b/docs/modules/ROOT/pages/cops_threadsafety.adoc
@@ -114,7 +114,7 @@ end
 
 | Enabled
 | Yes
-| Yes (Unsafe)
+| Always (Unsafe)
 | -
 | -
 |===
diff --git a/spec/rubocop/thread_safety_spec.rb b/spec/rubocop/thread_safety_spec.rb
index 544495b..7f84972 100644
--- a/spec/rubocop/thread_safety_spec.rb
+++ b/spec/rubocop/thread_safety_spec.rb
@@ -2,6 +2,6 @@
 
 RSpec.describe RuboCop::ThreadSafety do
   it 'has a version number' do
-    expect(RuboCop::ThreadSafety::VERSION).not_to be nil
+    expect(RuboCop::ThreadSafety::VERSION).not_to be_nil
   end
 end
(END)

Fixed (probably) by #37, feel free to close if I'm wrong