Corrects the title for percentage of + reviews

The current title "+/- ratio" is incorrect. The percentage being
shown is the percentage of + reviews over all reviews not - reviews.

Change-Id: Ib14890a2d35f0f0f93a0d098da5542e5f87a07d9
Closes-Bug: 1332141
Merge "Corrects the title for percentage of + reviews"