gql tests are failing with graphql-core 3.1.5 (cosmetic)

[leszekhanusz]

With graphql-core version 3.1.5:

• print_ast() break arguments over multiple lines
• the check for the source argument was changed

Some gql tests are failing now because of this.

Calling gql with an int instead of a string will generate a TypeError with object of type 'int' has no len() instead of body must be a string