Correct rendering::engine category slug

Cargo.toml

@@ -7,7 +7,7 @@ homepage = "https://github.com/gwihlidal/vk-sync-rs"
 repository = "https://github.com/gwihlidal/vk-sync-rs"
 documentation = "https://docs.rs/vk-sync"
 description = "Simplification of core Vulkan synchronization mechanisms such as pipeline barriers and events."
-categories = ["api-bindings", "rendering", "rendering::engines", "rendering::graphics-api", ]
+categories = ["api-bindings", "rendering", "rendering::engine", "rendering::graphics-api", ]
 keywords = ["vulkan", "vk", "ash", "graphics", "3d"]
 readme = "README.md"
 exclude = [