Fixed issue #19 - config_backup() is a function instead property

[tchellomello]

Fixed issue #19 that should be a function instead a @Property

» amcrest-cli  --camera amcrestcam1 --config-backup --save /tmp/cfg                                                                                 ~/d/h/homeassistant
Traceback (most recent call last):
  File "/home/mdemello/.virtualenvs/home_assistant/bin/amcrest-cli", line 863, in <module>
    main()
  File "/home/mdemello/.virtualenvs/home_assistant/bin/amcrest-cli", line 849, in main
    camera.config_backup(args.save)
TypeError: 'str' object is not callable

After applying the fix:

~ » amcrest-cli --camera amcrestcam1  --config-backup --save /tmp/lala22.txt 
~ » ls -la /tmp/lala22.txt                    
-rw-rw-r--. 1 user user 154734 Dec 14 19:23 /tmp/lala22.txt

[mention-bot]

@tchellomello, thanks for your PR! By analyzing the history of the files in this pull request, we identified @dougsland to be a potential reviewer.