Fix Explicitly Passing API Key to DeepgramClient

[davidvonthenen]

Proposed changes

Addresses issue: #283

Fix Explicitly Passing API Key to DeepgramClient. The bug was due to switching the "empty" API key from "", to None, empty. We will always just deal with the API key in terms of "".

Tested without environment variables and also made sure that the the environment variable method is unaffected.

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Further comments

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