v1.2.1

This patch primarily fixes the bug where the API and the CLI can crash when there is no network access to unpkg.com when creating single-file HTML readalongs.

🐛 Bug Fixes

• ff3c300 - update fallback bundles to web-component v1.5.2 (commit by @joanise)
• 015bfc6 - fail gracefully when we cannot connect to unpkg.com (commit by @joanise)
• b79e821 - exclude bundles from pre-commit filters (commit by @joanise)

⚡ Performance Improvements

• 301a46a - remove soundswallower from Heroku reqs (commit by @joanise)

♻️ Refactors

• 3896a63 - move alignment file i/o functions to align_util.py (commit by @joanise)