moved using statements

Author: The-Nutty

src/AngleSharp.Css.Tests/Values/UnitConversion.cs

@@ -1,9 +1,8 @@
-using System;
-
 namespace AngleSharp.Css.Tests.Values
 {
     using AngleSharp.Css.Values;
     using NUnit.Framework;
+    using System;
 
     [TestFixture]
     public class UnitConversionTests

src/AngleSharp.Css/IRenderDimensions.cs

@@ -1,7 +1,7 @@
-using System;
-
 namespace AngleSharp.Css
 {
+    using System;
+
     /// <summary>
     /// Represents the render settings for an element, used to calculate relative sizes (E.G. %, rem).
     /// </summary>