Fix c++98 mode compilation for parallel_utils_test.cc

Change-Id: I009032978bca910704c52f4de693d04fa13c6e07

internal/ceres/parallel_utils_test.cc

diff --git a/internal/ceres/parallel_utils_test.cc b/internal/ceres/parallel_utils_test.cc
index f997d25..8638f90 100644
--- a/internal/ceres/parallel_utils_test.cc
+++ b/internal/ceres/parallel_utils_test.cc
@@ -42,7 +42,7 @@
 // indices that are in-range and unique.
 TEST(LinearIndexToUpperTriangularIndexTest, UniqueAndValid) {
   for (int n = 0; n < 100; n++) {
-    std::set<std::pair<int, int>> seen_pairs;
+    std::set<std::pair<int, int> > seen_pairs;
     int actual_work_items = (n * (n + 1)) / 2;
     for (int k = 0; k < actual_work_items; k++) {
       int i, j;