fix: use `child_process.spawn` to better handle whitespace in command

[jonz94]

Closes #26

• Replace child_process.exec with child_process.spawn to better handle whitespace in command.
  • child_process.spawn will handle the character escaping for us, and it works seamlessly across all major OS.
• Add spawnCommand helper function
  • It converts child_process.spawn to a Promise based API with input/output behavior similar to executeCommand helper function.
  • The implementation is modified from this stackover answer: https://stackoverflow.com/a/67379845/9979122.