select 2 is used on all as: :select fields, I need to use normal select

[robertoboldi]

Hello why select2 is forced an all the select fields of my admin page?
f.input :block_type, as: :select, :label => "Tipo Blocco", :collection => NewsItemBlock.block_types, input_html: {class: 'js-block-type-selector'}

I need this input to be a normal select, but the gem forces this to be a :select2 input.
as you can see in my uploaded image it is a typical select2 form, while i need a normal select.

please help me!