fix (#461)

src/WireMock.Net/RequestMessage.cs

@@ -32,6 +32,11 @@ namespace WireMock
         /// </summary>
         public string AbsoluteUrl { get; }
 
+        /// <summary>
+        /// The ProxyUrl (if a proxy is used).
+        /// </summary>
+        public string ProxyUrl { get; set; }
+
         /// <summary>
         /// Gets the DateTime.
         /// </summary>