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.