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_modem_simple_proxy.h b/mock_modem_simple_proxy.h
index 6a2adf7..e08055b 100644
--- a/mock_modem_simple_proxy.h
+++ b/mock_modem_simple_proxy.h
@@ -15,7 +15,7 @@
 class MockModemSimpleProxy : public ModemSimpleProxyInterface {
  public:
   MockModemSimpleProxy();
-  virtual ~MockModemSimpleProxy();
+  ~MockModemSimpleProxy() override;
 
   MOCK_METHOD3(GetModemStatus, void(Error *error,
                                     const DBusPropertyMapCallback &callback,