fix: resolved npm_execpath issue

[MathurAditya724]

Closes #52

• Used event listener for the package manager.
• Updated the hooks function to replace the $npm_execpath in package.json file.
• Added === (triple equal sign) instead of == (double equal sign).

If the users haven't said yes to installation, we may not be able to get the package manager. For that, I have made npm the default value.

[yusukebe]

LGTM!

[yusukebe]

@MathurAditya724

Awesome! Let's ship it.