Upgrade gflags to master

Merge commit 'cb7bb2b58469b0ba5132fbcf4893b2ca76dead1c' into master

Change-Id: Id6b07c15b3bef794984d6f326d6596f043d1dde5
diff --git a/y2018/control_loops/superstructure/arm/dynamics.h b/y2018/control_loops/superstructure/arm/dynamics.h
index 3624f58..cdbd6fe 100644
--- a/y2018/control_loops/superstructure/arm/dynamics.h
+++ b/y2018/control_loops/superstructure/arm/dynamics.h
@@ -4,7 +4,7 @@
 #include "Eigen/Dense"
 
 #include "frc971/control_loops/runge_kutta.h"
-#include "third_party/gflags/include/gflags/gflags.h"
+#include "gflags/gflags.h"
 
 DECLARE_bool(gravity);