docs(tokens): fix typo in readme file

[SalimBensiali]

Contributing to Twilio

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paste-theme-designer – ./

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paste – ./

🔍 Inspect: https://vercel.com/twilio-dsys/paste/9oeks4acg
✅ Preview: https://paste-git-fork-salimbensiali-patch-1.twilio-dsys.vercel.app

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[TheSisb]

Thanks!