Fix Style/WordArray for subarrays

[fatkodima]

In #11334, I introduced a bug for nested arrays 😐

[['one', 'One'], 2, 3]

     Failure/Error: parent.values.any? { |subarray| complex_content?(subarray.values) }

     NoMethodError:
       undefined method `values' for s(:int, 2):RuboCop::AST::IntNode
       Did you mean?  value
     # ./lib/rubocop/cop/style/word_array.rb:103:in `block in within_2d_array_of_complex_content?'
     # ./lib/rubocop/cop/style/word_array.rb:103:in `any?'
     # ./lib/rubocop/cop/style/word_array.rb:103:in `within_2d_array_of_complex_content?'
     # ./lib/rubocop/cop/style/word_array.rb:88:in `on_array'
     # ./lib/rubocop/cop/commissioner.rb:101:in `public_send'
     # ./lib/rubocop/cop/commissioner.rb:101:in `block (2 levels) in trigger_responding_cops'
     # ./lib/rubocop/cop/commissioner.rb:165:in `with_cop_error_handling'
     # ./lib/rubocop/cop/commissioner.rb:100:in `block in trigger_responding_cops'
     # ./lib/rubocop/cop/commissioner.rb:99:in `each'
     # ./lib/rubocop/cop/commissioner.rb:99:in `trigger_responding_cops'
     # ./lib/rubocop/cop/commissioner.rb:69:in `on_array'

[bbatsov]

Thanks!