Merge pull request #240 from josh/fix-leaked-global-const

Fix leaked global constant

Author: Robert Mosolgo

lib/graphql/boolean_type.rb

@@ -1,10 +1,7 @@
 GraphQL::BOOLEAN_TYPE = GraphQL::ScalarType.define do
-  # Everything else is nil
-  ALLOWED_INPUTS = [true, false]
-
   name "Boolean"
   description "Represents `true` or `false` values."
 
-  coerce_input -> (value) { ALLOWED_INPUTS.include?(value) ? value : nil }
+  coerce_input -> (value) { (value == true || value == false) ? value : nil }
   coerce_result -> (value) { !!value }
 end