Fix type for case blueviolet (#14434)

The 'v' in this case was uppercase causing this typeconverter to reject BlueViolet as a valid color value. Fixes #AB1286706 [XVS]XLS0431: Invalid value for property 'BackgroundColor': 'BlueViolet'

Xamarin.Forms.Core/ColorTypeConverter.cs

@@ -149,7 +149,7 @@ public override object ConvertFromInvariantString(string value)
 							return Color.BlanchedAlmond;
 						case "blue":
 							return Color.Blue;
-						case "blueViolet":
+						case "blueviolet":
 							return Color.BlueViolet;
 						case "brown":
 							return Color.Brown;