mscMMN

Bug: Environment variable PORT is named EXPOSED_PORT in sample env file

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This environment variable `PORT` is not set in the supplied sample env file: https://github.com/standardnotes/syncing-server/blob/b46dad76324a1bc24888aeb8100c47e812ef966a/config/puma.rb#L12 Instead it's named `EXPOSED_PORT`. https://github.com/standardnotes/syncing-server/blob/d76615c53cf36af41a66ca0da669a970e66073ec/.env.sample#L10 Please review my proposed changes: https://github.com/standardnotes/syncing-server/pull/169