Add a missing using std::max and std::min.

Thanks to Philipp Bender for reporting this.

Change-Id: I1f2947d378e0e98f6d225126a686d52738df3df0

internal/ceres/coordinate_descent_minimizer.cc

diff --git a/internal/ceres/coordinate_descent_minimizer.cc b/internal/ceres/coordinate_descent_minimizer.cc
index 0c58329..e3a7a8e 100644
--- a/internal/ceres/coordinate_descent_minimizer.cc
+++ b/internal/ceres/coordinate_descent_minimizer.cc
@@ -53,6 +53,8 @@
 namespace internal {
 
 using std::map;
+using std::max;
+using std::min;
 using std::set;
 using std::string;
 using std::vector;