Update react-apollo.md

[mattphoto]

function declarations are hoisted but classes are not. So when one passes a class into withApollo HOC, the export statement must be below the class declaration. Switching the order in the example code will avoid users from running into this issue.

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]

@mattphoto: 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]

Agreed - thanks @mattphoto!