[ImgBot] Optimize images

*Total -- 553.76kb -> 514.49kb (7.09%)

/static/img/tutorials/ml/random-forest-feature-importance.jpg -- 81.42kb -> 69.77kb (14.32%)
/static/img/tutorials/ml/comparing-underfitting-balanced-fit-and-overfitting.jpg -- 102.46kb -> 93.93kb (8.33%)
/static/img/tutorials/ml/recursive-feature-elimination.jpg -- 114.90kb -> 107.07kb (6.81%)
/static/img/tutorials/ml/cancer-detection.jpg -- 98.77kb -> 92.96kb (5.88%)
/static/img/tutorials/ml/bubble-visualization.jpg -- 99.92kb -> 94.77kb (5.16%)
/static/img/tutorials/ml/probability-mass-function.jpg -- 56.29kb -> 56.00kb (0.53%)

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