[ImgBot] Optimize images (#10)

*Total -- 162.94kb -> 104.76kb (35.71%)

/res/preview.png -- 142.79kb -> 88.29kb (38.17%)
/res/task.png -- 6.79kb -> 5.30kb (22.05%)
/res/icon.png -- 5.01kb -> 3.92kb (21.69%)
/res/vscode.png -- 8.35kb -> 7.25kb (13.13%)

Signed-off-by: ImgBotApp <[email protected]>
Co-authored-by: ImgBotApp <[email protected]>

Author: imgbot[bot]