Fix: isLeafType matches type definition.

Based on GraphQL.js change: graphql/graphql-js@12b2137
Fixes #105.

Author: obi1kenobi

graphql/type/definition.py

@@ -41,8 +41,7 @@ def is_output_type(type):
 
 
 def is_leaf_type(type):
-    named_type = get_named_type(type)
-    return isinstance(named_type, (
+    return isinstance(type, (
         GraphQLScalarType,
         GraphQLEnumType,
     ))

graphql/validation/rules/scalar_leafs.py

@@ -1,5 +1,5 @@
 from ...error import GraphQLError
-from ...type.definition import is_leaf_type
+from ...type.definition import get_named_type, is_leaf_type
 from .base import ValidationRule
 
 
@@ -11,7 +11,7 @@ def enter_Field(self, node, key, parent, path, ancestors):
         if not type:
             return
 
-        if is_leaf_type(type):
+        if is_leaf_type(get_named_type(type)):
             if node.selection_set:
                 self.context.report_error(GraphQLError(
                     self.no_subselection_allowed_message(node.name.value, type),