Fix OKLAB to_string() to be 3 chars

Really to_string() should be replaced with it's actual name, and there
should be a new function called "channels()"

src/lib.rs

@@ -171,8 +171,8 @@ impl ToString for Space {
             Space::XYZ => String::from("xyz"),
             Space::LAB => String::from("lab"),
             Space::LCH => String::from("lch"),
-            Space::OKLAB => String::from("oklab"),
-            Space::OKLCH => String::from("oklch"),
+            Space::OKLAB => String::from("lab"),
+            Space::OKLCH => String::from("lch"),
         }
     }
 }