Added missing #prefix# markers to getUsersWhoFavoritedMostOfYourPosts()

This fixes database query error:

> Database error! ThinkUp could not execute the following query: SELECT * FROM ( SELECT u.*, count(f.post_id) AS total_likes from tu_favorites f INNER JOIN tu_users u ON u.user_id = f.fav_of_user_id INNER JOIN tu_posts p ON f.post_id = p.post_id WHERE f.author_user_id = :author_user_id and f.network=:network AND p.pub_date >= date_sub(current_date, INTERVAL :last_x_days day) GROUP BY f.fav_of_user_id ORDER BY total_likes DESC) favs WHERE favs.total_likes > 1 LIMIT 3 PDOException: SQLSTATE[42S02]: Base table or view not found: 1146 Table 'ivuorinen.tu_favorites' doesn't exist

Triggered by ``BiggestFansInsight::generateInsight``
Merge pull request #1591 from ivuorinen/patch-1

Added missing #prefix# markers to getUsersWhoFavoritedMostOfYourPosts()