Allow installation on 5.x branch #30

This change by @sgiehl removed support for the Matomo 5.x branch.

However, based on the comment "no code changes were needed", I guessed that the plugin would work fine on Matomo 5.x, and I can confirm it installs and works correctly on the latest 5.x release (5.14.1). I've attached a screenshot of the Matomo web UI:

And here is the environment variable in the container:

env | grep -i trust
MATOMO_GENERAL_TRUSTED_HOSTS=["example.org", "localhost.org"]

Would it be possible to restore support for the 5.x branch? I'm happy to do more testing if required.