Clean up deprecation warnings

Summary:Clean up a deprecation warning for JSONSchema's use of
Singleton. This is in experimental, so the interface change should be
reasonable..

Reviewed By: agoder

Differential Revision: D3203348

fb-gh-sync-id: 3283c7d9c507a545f3217eb5afc3734eb047b833
fbshipit-source-id: 3283c7d9c507a545f3217eb5afc3734eb047b833

folly/experimental/JSONSchema.cpp

@@ -1020,6 +1020,8 @@ std::unique_ptr<Validator> makeValidator(const dynamic& schema) {
   return std::move(v);
 }
 
-Validator* makeSchemaValidator() { return schemaValidator.get(); }
+std::shared_ptr<Validator> makeSchemaValidator() {
+  return schemaValidator.try_get();
+}
 }
 }

folly/experimental/JSONSchema.h

@@ -68,6 +68,6 @@ std::unique_ptr<Validator> makeValidator(const dynamic& schema);
  * Makes a validator for schemas. You should probably check your schema with
  * this before you use makeValidator().
  */
-Validator* makeSchemaValidator();
+std::shared_ptr<Validator> makeSchemaValidator();
 }
 }