Update doc comment.

Author: Cesar Blum Silveira

src/Microsoft.AspNetCore.Http.Abstractions/HttpRequest.cs

@@ -74,7 +74,7 @@ public abstract class HttpRequest
         /// This property is not used internally for routing or authorization decisions. It has not
         /// been UrlDecoded and care should be taken in its use.
         /// </remarks>
-        /// <returns></returns>
+        /// <returns>The raw request target.</returns>
         public abstract string RawTarget { get; set; }
 
         /// <summary>