chore(cli): fix missing single quote

[rayou]

Fix missing quote in python post-installed message.

Before

Initializing a new git repository...
Please run python3 -m venv .env'!
Executing Creating virtualenv...

After

Initializing a new git repository...
Please run 'python3 -m venv .env'!
Executing Creating virtualenv...

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[ghost]

Taking a step back, the Toolkit executes the command given in the message; the user doesn't need to. This message could probably be removed entirely.

[mergify]

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildProject6AEA49D1-qxepHUsryhcu
• Commit ID: 4a40fb7
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[mergify]

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).