Make content type checking less strict

[symm]

Thanks for making graphql-java-spring 👍

I've run into an issue when a doing a query with a content-type of application/json;charset=UTF-8. The GraphQLController rejects the request because strict matching does not like the ;charset=UTF-8 on the end

This PR updates both controllers to be less strict when checking the incoming content type.

[marceloverdijk]

I think #13 already solves this.

[symm]

Thanks @marceloverdijk I opened this smaller change because I saw no activity on that PR since 27 Jun. Happy if either gets merged as long as it gets fixed :)