Fixed some code issues

RGB.NET.Brushes/Gradients/AbstractGradient.cs

@@ -8,7 +8,8 @@ using RGB.NET.Core;
 
 namespace RGB.NET.Brushes.Gradients
 {
-    /// <inheritdoc />
+    /// <inheritdoc cref="AbstractDecoratable{T}" />
+    /// <inheritdoc cref="IGradient" />
     /// <summary>
     /// Represents a basic gradient.
     /// </summary>

RGB.NET.Brushes/Gradients/RainbowGradient.cs

@@ -5,7 +5,8 @@ using RGB.NET.Core;
 
 namespace RGB.NET.Brushes.Gradients
 {
-    /// <inheritdoc />
+    /// <inheritdoc cref="AbstractDecoratable{T}" />
+    /// <inheritdoc cref="IGradient" />
     /// <summary>
     /// Represents a rainbow gradient which circles through all colors of the HUE-color-space.<br />
     /// See <see href="http://upload.wikimedia.org/wikipedia/commons/a/ad/HueScale.svg" /> as reference.