Add `yarn pnp` support

Currently if you are using yarn pnp with this package, you will (understandably) get this error message:
```
Attempting to initialize using the npm package cz-conventional-changelog
Error: Could not locate node_modules in your project's root directory. Did you forget to npm init or npm install?
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received undefined
```
This is after installing commitizen locally via:
```
yarn add -D commitizen
```
and then running to following init command:
```
yarn dlx commitizen init cz-conventional-changelog --yarn --save-dev --save-exact
```

This is because `yarn pnp` does not use node_modules folder to install it's packages.

Reproduce el fallo con la instalación de Yarn PnP y el comando init mostrados; después, sigue la ruta de inicialización que comprueba si existe un directorio llamado node_modules. Se considera terminado cuando el mismo comando se completa con Yarn PnP sin requerir node_modules; añade o actualiza la cobertura de ese flujo si el repositorio tiene una ubicación de pruebas relevante.

Escrito por el modelo de indexación a partir del texto del issue.