Use linter when AST schema is unsuccessfully produced

[btoo]

Would be nice to use a linter like graphql-schema-linter when the provided graphql code is unsuccessfully parsed to tell the users why graphql-zeus isnt proceeding. I'm hoping this would be a better UX than just dumping the whole contents of the graphql code onto the command line

[aexol]

Of course we should do that. I have already implemented this kind of validation in new version of graphql-editor. Can you contribute copy it to zeus?