Avoid signed/unsigned warning in VC++ 2017 builds

test/unittests/base/iterator-unittest.cc

Index: test/unittests/base/iterator-unittest.cc
diff --git a/test/unittests/base/iterator-unittest.cc b/test/unittests/base/iterator-unittest.cc
index 8da26ce20eedc4767c80490d4c502f8046a37673..c5fe7bc5055648fe255bd82d4acb77dec9727577 100644
--- a/test/unittests/base/iterator-unittest.cc
+++ b/test/unittests/base/iterator-unittest.cc
@@ -42,7 +42,7 @@ TEST(IteratorTest, IteratorRangeArray) {
 
 
 TEST(IteratorTest, IteratorRangeDeque) {
-  typedef std::deque<unsigned> C;
+  typedef std::deque<int> C;
   C c;
   c.push_back(1);
   c.push_back(2);