[ImgBot] Optimize images

*Total -- 853.26kb -> 748.12kb (12.32%)

/graphs/web2/response-time-day.png -- 11.26kb -> 2.94kb (73.92%)
/graphs/web6/response-time-day.png -- 11.74kb -> 4.44kb (62.2%)
/graphs/web4/response-time-day.png -- 10.80kb -> 4.08kb (62.19%)
/graphs/thundersquared/response-time-day.png -- 12.24kb -> 4.64kb (62.08%)
/graphs/web7/response-time-day.png -- 11.14kb -> 4.46kb (59.95%)
/graphs/web5/response-time-day.png -- 10.29kb -> 4.39kb (57.33%)
/graphs/web1/response-time-day.png -- 8.03kb -> 4.14kb (48.41%)
/graphs/web4/response-time-week.png -- 15.46kb -> 13.14kb (15.02%)
/graphs/web6/response-time-week.png -- 15.32kb -> 13.06kb (14.75%)
/graphs/thundersquared/response-time-week.png -- 15.00kb -> 12.97kb (13.57%)
/graphs/web2/response-time-week.png -- 14.97kb -> 13.01kb (13.08%)
/graphs/web5/response-time-week.png -- 15.60kb -> 13.75kb (11.86%)
/graphs/web1/response-time-week.png -- 15.19kb -> 13.40kb (11.75%)
/graphs/web7/response-time-week.png -- 14.28kb -> 12.61kb (11.73%)
/graphs/web6/response-time-year.png -- 35.39kb -> 31.72kb (10.38%)
/graphs/web6/response-time.png -- 35.39kb -> 31.72kb (10.38%)
/graphs/web2/response-time-year.png -- 35.61kb -> 31.97kb (10.24%)
/graphs/web2/response-time.png -- 35.61kb -> 31.97kb (10.24%)
/graphs/web6/response-time-month.png -- 23.13kb -> 20.86kb (9.84%)
/graphs/web7/response-time-year.png -- 39.81kb -> 36.48kb (8.35%)
/graphs/web7/response-time.png -- 39.81kb -> 36.48kb (8.35%)
/graphs/web4/response-time-month.png -- 25.60kb -> 23.62kb (7.73%)
/graphs/web2/response-time-month.png -- 26.40kb -> 24.44kb (7.42%)
/graphs/web7/response-time-month.png -- 25.62kb -> 23.72kb (7.41%)
/graphs/thundersquared/response-time.png -- 40.09kb -> 37.26kb (7.07%)
/graphs/thundersquared/response-time-year.png -- 40.09kb -> 37.26kb (7.07%)
/graphs/thundersquared/response-time-month.png -- 26.49kb -> 24.73kb (6.63%)
/graphs/web1/response-time-month.png -- 26.39kb -> 24.79kb (6.07%)
/graphs/web5/response-time-year.png -- 40.24kb -> 38.18kb (5.12%)
/graphs/web5/response-time.png -- 40.24kb -> 38.18kb (5.12%)
/graphs/web5/response-time-month.png -- 26.90kb -> 25.74kb (4.31%)
/graphs/web4/response-time-year.png -- 24.04kb -> 23.56kb (1.96%)
/graphs/web4/response-time.png -- 24.04kb -> 23.56kb (1.96%)
/graphs/web1/response-time-year.png -- 30.52kb -> 30.41kb (0.35%)
/graphs/web1/response-time.png -- 30.52kb -> 30.41kb (0.35%)

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