[Typescript] Date-Array query Parameter not serialized correctly

Description

Hi,

I have the following problem when using a Date-Array-Parameter in my swagger file:

The generated client is not serializing the dates correctly and the server is returning Bad request: Validation errors.
For example:
The client generates: createdAfter= Thu%20Mar%2008%202018%2015:56:22%20GMT%2B0100%20(CET), Thu%20Mar%2008%202018%2015:56:22%20GMT%2B0100%20(CET),
instead of;
createdAfter=2018-03-08T15:56:22Z,2018-03-08T15:56:22Z

Everything is working perfectly fine, if I only have a single date-query-parameter.

Swagger-codegen version

2.3.1

Swagger declaration file content or url

This is the relevant part of my swagger file:

parameters:
        - name: createdAfter
          in: query
          required: false
          type: array
          items:
            type: string
            format: date-time

Command line used for generation

java -jar libs/swagger-codegen-cli-2.3.1.jar generate -i src/api/swagger/swagger.yaml -l typescript-angular -o ~/swaggerGeneratedCode/typescript-angular/ --additional-properties=modelPropertyNaming=original

Suggest a fix/enhancement

I think, I already found the problem.
This is my generated code:
queryParameters = queryParameters.set('createdAfter', createdBefore.join(COLLECTION_FORMATS['csv']));

We have to call toISOString(). So it should be something like:
queryParameters = queryParameters.set('createdAfter', createdAfter.map((i) => i.toISOString()).join(COLLECTION_FORMATS['csv']));

This line in the template is generating the wrong code:
https://github.com/swagger-api/swagger-codegen/blob/f00a1ef52c7d478436711b1796eb1cc1aa1de09d/modules/swagger-codegen/src/main/resources/typescript-angular/api.service.mustache#L146-L148

A check is already there for single date-parameters a few lines below:
https://github.com/swagger-api/swagger-codegen/blob/f00a1ef52c7d478436711b1796eb1cc1aa1de09d/modules/swagger-codegen/src/main/resources/typescript-angular/api.service.mustache#L153-L155

So I guess, in case of date-array-params the template code should be something like:
{{#useHttpClient}}queryParameters = {{/useHttpClient}}queryParameters.set('{{baseName}}', {{paramName}}.map((i) => i.toISOString()).join(COLLECTION_FORMATS['{{collectionFormat}}']));

(just added .map((i) => i.toISOString()))

What is missing for a fix, is a test for the child-elements of the listContainer if they are of type date. I have no idea how to implement that in mustache-templates.

Please help and thanks in advance.

Start with modules/swagger-codegen/src/main/resources/typescript-angular/api.service.mustache, comparing array serialization around lines 146-148 with the single-date handling around lines 153-155. Locate the typescript-angular generator tests and add coverage for date child elements in listContainer; done means generated query parameters use ISO date strings and the test passes.