spec: reducers set parameters as an array

[glowcloud]

Describe the bug you're encountering

The value set in UPDATE_PARAM reducer

swagger-ui/src/core/plugins/spec/reducers.js

Line 56 in 3a86443

[UPDATE_PARAM]: ( state, {payload} ) => {

for multi-value parameters is an array, while the expected type of the set value is an Immutable List.

To reproduce...

Steps to reproduce the behavior:

1. Add a console.log(List.isList(value)) to the reducer
2. Load the default Petstore definition
3. Scroll down to /pet/findByStatus
4. Try it out with at least one value chosen
5. Open console and see false

Expected behavior

The value should be converted from an array to an Immutable List in the reducer.

[char0n]

Addressed in #9567