Update 04.md - minor text update

[heypano]

Official docs no longer use classes for the tic tac toe example

[heypano]

@kentcdodds just added this minor update since the official react docs have been updated now

[heypano]

Thanks for this! Could you update the PR to not include your changes in the .js?

oops! sorry about that @kentcdodds -- updated!

[kentcdodds]

@all-contributors please add @heypano for docs

[allcontributors[bot]]

@kentcdodds

I've put up a pull request to add @heypano! :tada: