Response example matches mutation name

[nandisc]

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This request fixes an name mismatch in the "Schema basics" tutorial. The section which focuses on creating explicit types for mutations references an earlier mutation which updates the user's email. The name of the referenced mutation is updateUserEmail, however the example API response uses the value updateUser which, as I understand it, should match the mutation name.

[apollo-cla]

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[nandisc]

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

I've taken care of this.

[glasser]

Sorry for the delay: it does appear that this PR is still valid, thanks!