fix: 更新邮件奖励图标

[alex3236]

resolves #870
邮件奖励已有 crop，无需使用完整图片作为识别元素

March7thAssistant/tasks/reward/__init__.py

Lines 31 to 34 in ad92725

	self.reward_mapping = {
	"mail": ("./assets/images/share/menu/mail_reward.png", 3000000, (1823.0 / 1920, 224.0 / 1080, 91.0 / 1920, 92.0 / 1080)),
	"assist": ("./assets/images/share/menu/assist_reward.png", 2000000, self.crop),