emulators/ppsspp: unbreak fetch by downgrading to 1.13.1

v1.13.1b (392d83fb2203) tag has been removed upstream.

> Attempting to fetch https://codeload.github.com/hrydgard/ppsspp/tar.gz/v1.13.1b?dummy=/hrydgard-ppsspp-v1.13.1b_GH0.tar.gz

fetch: https://codeload.github.com/hrydgard/ppsspp/tar.gz/v1.13.1b?dummy=/hrydgard-ppsspp-v1.13.1b_GH0.tar.gz: Not Found

Reported by: pkg-fallout

This reverts commit 93e17d50eb23572b334f4a42fa1ae5e6d4a52400.