The webpack-md5-hash plugin attempts to make the generated hashes
less susceptible to churn when chunks haven't actually changed.
However it requires careful use and clearly wasn't set up correctly,
since the manifest file hashes were always the same regardless of
content, causing stale files and runtime errors in production.
Once Neutrino v6 is released, we can use its new in-built support
for caching to save having to implement this ourselves.