Update getToken from functinosOauthClient

[luskin]

The sample code shows to set the results of getToken directly to the variable tokens however tokens is now a property of the response so you need to store the tokens object from within the response as google states here:

https://github.com/google/google-api-nodejs-client:

const {tokens} = await oauth2Client.getToken(code)
oauth2Client.setCredentials(tokens);

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[luskin]

I have signed it!

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CLAs look good, thanks!

[nicolasgarnier]

Thanks @luskin !