Normalize the Python package name to "google-generativeai"

[doggy8088]

Description of the change

The package name google-generativeai was written as google.generativeai which is incorrect.

Motivation

Use the correct package name on the pip install command.

Type of change

Choose one: Bug fix

Checklist

• I have performed a self-review of my code.
• I have added detailed comments to my code where applicable.
• I have verified that my change does not break existing code.
• My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• I am familiar with the Google Style Guide for the language I have coded in.
• I have read through the Contributing Guide and signed the Contributor License Agreement.

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[MarkDaoust]

That is the official name. Thanks.