Noticed compiler warning C4800: 'double': forcing value to bool 'true' or…

Noticed compiler warning C4800: 'double': forcing value to bool 'true' or 'false' (performance warning) (#538)

- suggesting to change the test to what perhaps was the original intention

dlib/test/elastic_net.cpp

@@ -109,7 +109,7 @@ namespace
                 results = basic_elastic_net(X, Y, ridge_lambda, lasso_budget*s, eps);
                 results2 = solver(ridge_lambda, lasso_budget*s);
                 dlog << LINFO << "error: "<< max(abs(results - results2));
-                DLIB_TEST(max(abs(results - results2) < 1e-3));
+                DLIB_TEST(max(abs(results - results2)) < 1e-3);
             }
         }
     } a;