Docker build badge broken

[maehr]

Describe the bug
The Docker badge in the README is broken.

To Reproduce
...

Expected behavior
Should go here https://hub.docker.com/r/maehr/typademic

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.