Update Gradio pinned versions in metrics for dark theme fix

[BramVanroy]

Dark themes on Gradio used to have a problem because special text (like code tags) were not legible (example below).

This was fixed in 3.1.7. Unfortunately many (all?) of the metrics spaces are still on older Gradio versions (like this one; 3.0.2) where the dark theme leads to a bad experience.

This should be easily fixable with a version bump in the README's of all metrics. I can add a PR for that but I am posting this issue first in case there might be incompatibilities with more recent Gradio versions.