support setting param type with a string.

[zw963]

Current worked version is:

 param :sku, type: String

But, I expect version is:

  param :sku, type:  'String'

In rails 5, use a constant in method argument result in eager laad, will broken somethings in dev. So, rails 5 with deperagate WARN for following example code:

has_many :order_notifications, class_name: Notification::Order   # bad
has_many :order_notifications, class_name: 'Notification::Order'   # good

[catmando]

type here is more similar to "class" in AR... in fact I think there is an issue to change it class. We could have type_name or class_name if needed...