[ImgBot] Optimize images

*Total -- 617.15kb -> 515.68kb (16.44%)

/graphs/google/response-time-day.png -- 11.21kb -> 2.64kb (76.5%)
/graphs/test-broken-site/response-time-year.png -- 9.60kb -> 3.99kb (58.41%)
/graphs/test-broken-site/response-time.png -- 9.60kb -> 3.99kb (58.41%)
/graphs/test-broken-site/response-time-month.png -- 1.17kb -> 0.49kb (57.86%)
/graphs/test-broken-site/response-time-day.png -- 1.17kb -> 0.49kb (57.86%)
/graphs/test-broken-site/response-time-week.png -- 1.17kb -> 0.49kb (57.86%)
/graphs/hacker-news/response-time-day.png -- 10.27kb -> 4.78kb (53.48%)
/graphs/wikipedia/response-time-day.png -- 6.90kb -> 3.74kb (45.83%)
/graphs/hacker-news/response-time-week.png -- 18.41kb -> 15.55kb (15.51%)
/graphs/wikipedia/response-time-week.png -- 17.91kb -> 15.14kb (15.45%)
/graphs/wikipedia/response-time.png -- 69.62kb -> 60.05kb (13.74%)
/graphs/wikipedia/response-time-year.png -- 69.62kb -> 60.05kb (13.74%)
/graphs/hacker-news/response-time-year.png -- 82.01kb -> 70.88kb (13.57%)
/graphs/hacker-news/response-time.png -- 82.01kb -> 70.88kb (13.57%)
/graphs/google/response-time.png -- 66.77kb -> 57.77kb (13.49%)
/graphs/google/response-time-year.png -- 66.77kb -> 57.77kb (13.49%)
/graphs/wikipedia/response-time-month.png -- 22.85kb -> 20.94kb (8.35%)
/graphs/google/response-time-week.png -- 16.75kb -> 15.37kb (8.21%)
/graphs/hacker-news/response-time-month.png -- 26.20kb -> 24.52kb (6.42%)
/assets/upptime-icon.svg -- 0.34kb -> 0.32kb (3.78%)
/graphs/google/response-time-month.png -- 26.81kb -> 25.83kb (3.67%)

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Author: ImgBotApp