Update execute notebook on startup script

[philipskokoh]

• Current SageMaker Notebook instance does not have pytorch_p36. It's pytorch_p37 now.
• The current nbconvert version requires explicit --to parameter.

Issue #, if available: The script is not working, and needs some modification.

Description of changes: Few modification to make the lifecycle configuration script work on the current SageMaker Notebook instance.

• Current SageMaker Notebook instance does not have pytorch_p36. It's pytorch_p37 now.
• The current nbconvert version requires explicit --to parameter.

Testing Done

• [x] Notebook Instance created successfully with the Lifecycle Configuration
• [x] Notebook Instance stopped and started successfully
• [ ] Documentation in the script around any network access requirements
• [ ] Documentation in the script around any IAM permission requirements
• [ ] CLI commands used to validate functionality on the instance
• [ ] New script link and description added to README.md

# Provide your commands here
/you/commands/here

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