fix(clean): make sure to delete node_modules as last item

[szymonrybczak]

Summary:

In this Pull Request I've moved npm to the end of list → removing node_modules at the end of clean command makes sure that we don't remove CLI itself before finish command 😅

Fixes #2353

Test Plan:

1. Clone the repository and do all the required steps from the Contributing guide
2. Run this command:

node /path/to/react-native-cli/packages/cli/build/bin.js clean

3. npm should be always as last item ✅

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md