ART: Fix linting errors

Fix bounds_check_elimination linting errors.

Change-Id: I040433ecbc84d740bff331c37df0bfcc64dc244e
diff --git a/compiler/optimizing/bounds_check_elimination.h b/compiler/optimizing/bounds_check_elimination.h
index 25551d5..05cb185 100644
--- a/compiler/optimizing/bounds_check_elimination.h
+++ b/compiler/optimizing/bounds_check_elimination.h
@@ -23,7 +23,7 @@
 
 class BoundsCheckElimination : public HOptimization {
  public:
-  BoundsCheckElimination(HGraph* graph) : HOptimization(graph, true, "BCE") {}
+  explicit BoundsCheckElimination(HGraph* graph) : HOptimization(graph, true, "BCE") {}
 
   void Run() OVERRIDE;