Round alpha values to 2DP

When converting hex colours such as #AABBCC11 to RGBA, the alpha value was being output as "0.067777776" for example which is a bit daft so round it off to 2DP to match other implementations

Author: lee-m

src/ExCSS/Values/Color.cs

@@ -270,7 +270,7 @@ public static Color FromHwba(float hue, float whiteness, float blackness, float
 
         public int Value => _hashcode;
         public byte A => _alpha;
-        public double Alpha => _alpha / 255.0;
+        public double Alpha => Math.Round(_alpha / 255.0, 2);
         public byte R => _red;
         public byte G => _green;
         public byte B => _blue;