<% if @product.subscribable? %>
  <%= hidden_field_tag (@product.variants_and_option_values.any? ? :quantity : "variants[#{@product.master.id}]"),
              1, :class => 'title' %>
<% else %>
  <%= number_field_tag (@product.variants_and_option_values.any? ? :quantity : "variants[#{@product.master.id}]"),
            1, :class => 'title', :min => 1 %>
<% end %>
<% if @product.subscribable? %>
  <%=  hidden_field_tag :quantity, 1, :class => 'title', :min => 1 %>
<% else %>
  <%=  number_field_tag :quantity, 1, :class => 'title', :min => 1 %>
<% end %>

Update number_field_tag to mach new spree syntax
Update number_field_tag to mach new spree syntax
