chore: pnpm, bump dependencies, and version → 0.1.1

- Uses `pnpm` instead of `npm`
- Bumps the outdated dependencies
- Renames `rollup.config.js` → `rollup.config.mjs` because new Rollup
  does not allow .js files to use ESM syntax unless the entire project
  is configured fore ESM
- Bumps version to 0.1.1

Author: kikuomax