fix avatar aspect ratios with object-fit: cover instead of fill
fix avatar aspect ratios with object-fit: cover instead of fill

fixes #115. tentatively assigning to @dshanske because he originally added `object-fit: fill` in d0ca8ed2aeb287bddca027322f9f91a61b0f9598.

dshanske/wordpress-semantic-linkbacks,pfefferle/wordpress-semantic-linkbacks,pfefferle/wordpress-semantic-linkbacks,dshanske/wordpress-semantic-linkbacks,dshanske/wordpress-semantic-linkbacks,dshanske/wordpress-semantic-linkbacks,pfefferle/wordpress-semantic-linkbacks,pfefferle/wordpress-semantic-linkbacks