Fix incorrect use of abs() function

test/weighted_matching_test2.cpp

@@ -181,7 +181,7 @@ void test_matching(const Graph& g, WeightType answer)
         {
             WeightType eps = std::numeric_limits<WeightType>::epsilon();
             WeightType max_error = std::max(eps, answer * eps);
-            same_answer = (abs(weight - answer) <= max_error);
+            same_answer = (std::abs(weight - answer) <= max_error);
         }
 
         BOOST_TEST(same_answer);