Change error response to the same as request text

src/main/groovy/pl/touk/mockserver/server/ContextExecutor.groovy

@@ -40,7 +40,7 @@ class ContextExecutor {
                     }
                 }
                 ex.sendResponseHeaders(404, 0)
-                ex.responseBody << "<invalidInput/>"
+                ex.responseBody << request.text
                 ex.responseBody.close()
         })
     }