missing swagger support for `spec/coll-of`

`spec-tools.visitor` has
`(defmethod visit-spec 'clojure.spec.alpha/coll-of ...)` which ends up dispatching on
```
(case type
:map-of ::map-of
:set ::set-of
:vector ::vector-of)
```
while there is no implementation of `accept-spec` for any of `#{::visitor/map-of, ::visitor/set-of, ::visitor/vector-of}`

I've tried to add a
```
(defmethod swagger/accept-spec ::vector-of [_ _ children _]
(println "CHILDREN-VECTOR-OF" (util/pp children))
{:enum children :type "string"})
```
this prints `CHILDREN-VECTOR-OF [{}]`

This leads me to suspect that the implementation of `visit-spec` for `clojure.spec.alpha/coll-of` is flawed.

Start in spec-tools.visitor at the visit-spec implementation for clojure.spec.alpha/coll-of, then trace the swagger/accept-spec dispatch for ::visitor/map-of, ::visitor/set-of, and ::visitor/vector-of. Reproduce the reported children value and determine what support is needed for each collection type; done means coll-of specs produce correct Swagger output without the missing dispatch or malformed children.

Written by the indexing model from the issue text.