add queryString for qs
add queryString for qs

here only encoding and limit

in co-body->form used qs module
return opts.qs.parse(str, opts.queryString);

qs will also limit specifying indices in an array to a maximum index of 20. Any array members with an index of greater than 20 will instead be converted to an object with the index as the key
dlau/koa-body