Bump SixLabors.ImageSharp from 2.1.3 to 2.1.8 in /src/Gym.Environments#21

dependabot[bot] wants to merge 1 commit intomasterSciSharp/Gym.NET:masterfrom

dependabot/nuget/src/Gym.Environments/SixLabors.ImageSharp-2.1.8SciSharp/Gym.NET:dependabot/nuget/src/Gym.Environments/SixLabors.ImageSharp-2.1.8Copy head branch name to clipboard