Include generation date in cache header.

Author: Daniel15

src/React/JsxTransformer.cs

@@ -157,8 +157,9 @@ private string GetFileHeader(string hash)
 @"{0}
 // Automatically generated by ReactJS.NET. Do not edit, your changes will be overridden.
 // Version: {1}
+// Generated at: {2}
 ///////////////////////////////////////////////////////////////////////////////
-", _fileCacheHash.AddPrefix(hash), _environment.Version);
+", _fileCacheHash.AddPrefix(hash), _environment.Version, DateTime.Now);
 		}
 
 		/// <summary>