Resources: Fix gradient on RetroAchievements icon

This logo (svg version) was originally done by @fffathur before he had a GitHub account. He recently touched up the file to fix some issues with the gradients and make it match the original much better.

Co-authored-by: fffathur <132241318+fffathur@users.noreply.github.com>

Author: 2 people