1.0.0-beta.4: `--open` flag to open dev-server in browser

What's Changed

• feat(abell): add option to open browser on start by @saurabhdaware in #167

  abell dev --open # opens localhost in browser

• fix(abell): fs.exists build error in windows by @saurabhdaware in #167

Full Changelog: v1.0.0-beta.3...abell-v1.0.0-beta.4