[ImgBot] Optimize images (#334)

*Total -- 90.34kb -> 61.77kb (31.63%)

/docs/images/Tutorial1.svg -- 10.08kb -> 6.33kb (37.19%)
/docs/images/FetchBeerFails.svg -- 9.00kb -> 5.93kb (34.13%)
/docs/images/FetchBeer2.svg -- 21.19kb -> 14.41kb (32%)
/docs/images/Tutorial2.svg -- 34.19kb -> 23.75kb (30.54%)
/docs/images/DecoratorEnterRoom.svg -- 15.88kb -> 11.35kb (28.54%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Co-authored-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: imgbot[bot]