Error when using primitive data type "file"

[MasonM]

The Swagger 2.0 spec supports having a Schema object with root type "file", which is an extension to JSON Schema:

As an extension to the Schema Object, its root type value may also be "file". This SHOULD be accompanied by a relevant produces mime-type.
https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#responseObject

Doing this results in an assertion failure with the message "is an invalid type for file". Here's a branch with a test case showing that: master...MasonM:bug-with-schema-file

Output on my machine:

$  ./vendor/bin/phpunit      
PHPUnit 6.2.4 by Sebastian Bergmann and contributors.

.E............................................................... 65 / 93 ( 69%)
............................                                      93 / 93 (100%)

Time: 93 ms, Memory: 10.00MB

There was 1 error:

1) FR3D\SwaggerAssertions\PhpUnit\AssertsTraitTest::testAssertResponseBodyMatchWithFile
JsonSchema\Exception\InvalidArgumentException: GIF89a,; is an invalid type for file

/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/TypeConstraint.php:143
/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/TypeConstraint.php:73
/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/Constraint.php:201
/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/UndefinedConstraint.php:130
/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/UndefinedConstraint.php:36
/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/Constraint.php:217
/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/SchemaConstraint.php:29
/Users/mmalone/src/SwaggerAssertions/vendor/justinrainbow/json-schema/src/JsonSchema/Validator.php:36
/Users/mmalone/src/SwaggerAssertions/src/PhpUnit/JsonSchemaConstraint.php:41
/Users/mmalone/src/SwaggerAssertions/src/PhpUnit/AssertsTrait.php:37
/Users/mmalone/src/SwaggerAssertions/tests/PhpUnit/AssertsTraitTest.php:43

ERRORS!
Tests: 93, Assertions: 211, Errors: 1.

[Maks3w]

Done