Language flags not working in Docker container

[ghostbear]

Steps to reproduce

1. Create a new Series
2. Open language dropdown

Expected behavior

A flag representing the language

Actual behavior

The unknown flag for all langauges

Logs

No response

Tankobon version

v0.0.1

Operating system

Docker

Other details

Failed to load resource: the server responded with a status of 403 (/flags/rectangle/SE.svg:1)

Acknowledgements

• [X] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• [X] I have written a short but informative title.
• [X] I have updated the app to the latest version.
• [X] I filled out all of the requested information in this form.