converts example/src/VoiceTest.tsx to function component

[sethcwhiting]

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I'm about to use this package on a project and the rest of my codebase uses function components instead of classes. I think the majority of people starting new projects will probably be doing the same. With this change, I will be able to work with this component the same way I work with all of my others. I'm happy to fix any errors you find. Thanks.

[safaiyeh]

THanks @sethcwhiting Ill test this out within the week