Don't use :eq() jQuery selector

This is probably more performant: http://jsperf.com/jquery-children-vs-eq

Real rationale for this commit is that the previous version was not supported by zepto (https://github.com/madrobby/zepto/blob/1d94d92223a5ec2edf1fbe18a7a9cc717e7663e4/src/zepto.js#L53-L56)