code sample reflects params for withClientState

[haysclark]

apollo-link-state's withClientState() method expects a string or array of typeDefs.

Users that copy and paste the previous code sample's typeDef object will encounter runtime warnings when it is parsed by withClientState(). This updated version parses correctly with no warnings and matches the apollo-link-state example code:
https://github.com/apollographql/apollo-link-state/blob/master/examples/todo/src/index.js#L13-L29

Checklist:

• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests

[apollo-cla]

@haysclark: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[hwillson]

Thanks @haysclark!