Add type inspection for PrimaryKeyRelatedField (#26)

Guess the type for PrimaryKeyRelatedField from the related ModelField.

tests/conftest.py

@@ -40,7 +40,7 @@ def swagger_dict(generator):
 
 
 @pytest.fixture
-def validate_schema():
+def validate_schema(db):
     def validate_schema(swagger):
         from flex.core import parse as validate_flex
         from swagger_spec_validator.validator20 import validate_spec as validate_ssv

tests/reference.yaml

@@ -1042,7 +1042,7 @@ definitions:
       snippets:
         type: array
         items:
-          type: string
+          type: integer
         uniqueItems: true
       last_connected_ip:
         description: i'm out of ideas