Update avatar container name so it doesnt conflict with other image containers

Bug from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7206 renders all wiki images circular   
Before:   
![Screen_Shot_2016-11-03_at_9.27.45_AM](/uploads/f49baa4481cec6d6c043087aa1a83d09/Screen_Shot_2016-11-03_at_9.27.45_AM.png)
After:   
![Screen_Shot_2016-11-03_at_9.27.37_AM](/uploads/5b21d1752b5fa5adcabd44b8973fb55d/Screen_Shot_2016-11-03_at_9.27.37_AM.png)

cc @tauriedavis @dzaporozhets 

See merge request !7268