Update Makefile

example/Makefile

@@ -15,4 +15,4 @@ unit_test: unit_test_driver.cpp ArrayList_tests.cpp ArrayList.cpp
 
 # --- clean destroys all the .o files
 clean:
-	-@rm -rf *.o *~ a.out 2>/dev/null
+	-@rm -rf *.o *~ core* a.out 2>/dev/null