fix the coverage badge by switching to the difference branch in the URL.
fix the coverage badge by switching to the difference branch in the URL.

berkmancenter/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud