message: Add heading callback mock
diff: @@ -9,6 +9,7 @@ class MockTelemetry {
  public:
  MOCK_CONST_METHOD1(subscribe_position, void(Telemetry::PositionCallback)){};
  MOCK_CONST_METHOD1(subscribe_health, void(Telemetry::HealthCallback)){};
  + MOCK_CONST_METHOD1(subscribe_heading, void(Telemetry::HeadingCallback)){};
  MOCK_CONST_METHOD1(subscribe_home, void(Telemetry::PositionCallback)){};
  MOCK_CONST_METHOD1(subscribe_in_air, void(Telemetry::InAirCallback)){};
  MOCK_CONST_METHOD1(subscribe_status_text, void(Telemetry::StatusTextCallback)){};
  