require 'active_support/core_ext' (#361)

* require 'active_support/core_ext'

`blank?' for array needs  require 'active_support/core_ext'

* require 'active_support' as well

ref: https://stackoverflow.com/questions/37850575/undefined-method-blank-for-123string-nomethoderror?

Co-authored-by: peter scholz <pscholz.le@gmail.com>

Author: pravi

lib/grape_entity/exposure/base.rb

@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 
+require 'active_support'
+require 'active_support/core_ext'
+
 module Grape
   class Entity
     module Exposure