Tetris should have sdlpp.hpp as dependency

Makefile

@@ -19,6 +19,8 @@ sdlpp.o: sdlpp.cpp sdlpp.hpp
 	$(CXX) $(CFLAGS) -c -o $@ $< ${LDFLAGS}
 test.o: tests/test.cpp sdlpp.hpp tests/catch.hpp
 	$(CXX) $(CFLAGS) -c -o $@ $< ${LDFLAGS}
+tetris.o: tetris.cpp sdlpp.hpp
+	$(CXX) $(CFLAGS) -c -o $@ $< ${LDFLAGS}
 
 clean:
 	rm -Rf *.o test demo