unit test to assert that README has latest version in demo

**Is your feature request related to a problem? Please describe.**
The README's unpkg demo is perpetually outdated

**Describe the solution you'd like**
The unit-test should assert that it isn't

**Describe alternatives you've considered**
Dynamically generated README

**Additional context**
See recent commits for an example of me forgetting until too late again: d5cf9ca
