shill: Add C++11 override specifier to destructors of derived classes.

BUG=None
TEST=`USE=wimax FEATURES=test emerge-$BOARD platform2`

Change-Id: I88d4e29165869b26924cccb94ac940dc8961c312
Reviewed-on: https://chromium-review.googlesource.com/212267
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
diff --git a/mock_ares.h b/mock_ares.h
index 0a89de2..95dae94 100644
--- a/mock_ares.h
+++ b/mock_ares.h
@@ -15,7 +15,7 @@
 class MockAres : public Ares {
  public:
   MockAres();
-  virtual ~MockAres();
+  ~MockAres() override;
 
   MOCK_METHOD1(Destroy, void(ares_channel channel));
   MOCK_METHOD5(GetHostByName, void(ares_channel channel,