Make sure no js error is thrown when clicking on Activity directory tabs

After r8378 the use of "." instead of "," at line 828 of buddypress.js file was causing a javascript error when clicking on the Activity directory tabs (All Members, My Friends, My Groups, My Favorites, Mentions).

Fixes #5661

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8446 cdf35c40-ae34-48e0-9cc9-0c9da1808c22