Fix broken compatibility link

This link was broken since a while.

I am not sure if the entire paragraph is meaningful, as in [655de4609](https://github.com/mozilla/fireplace/commit/655de46095bbe181d5afed54842e99fcc477d5ed) Fireplace has removed the entire compatibility library with the message "upgrade to bower", but I kind of missing where was it moved (if at all).
Currently Fireplace [doesn't have that functionality](https://github.com/mozilla/fireplace/search?q=itervalues), so, unless some of added Bower libraries implement it ([don't see that](https://github.com/mozilla/fireplace/commit/655de46095bbe181d5afed54842e99fcc477d5ed#diff-0a08a7565aba4405282251491979bb6bR5)), the functionality was removed.