[Typescript] Multiple interface inheritance broken

Description

Issue was introduced from version 2.4.14 to 2.4.15.
2.4.14: Swagger 2.0 type refs were resolved correctly and members from multiple refs were pasted into the generated interface.
2.4.15: Refs are now translated as interface extensions but with multiple refs only one interface is extended

E.g.

UserPermissions:
   type: object
   allOf:
     - $ref: "#/definitions/PermissionUser"
     - $ref: "../definitions/authz.yml#/definitions/PermissionsWithChanges"

translates to

export interface UserPermissions extends PermissionUser {
}

Swagger-codegen version

2.4.15

Command line used for generation

docker run --rm -v ${PWD}:/local swaggerapi/swagger-codegen-cli:2.4.15 generate -i $BASE_URL/swagger.yml -l typescript-aurelia -o /local/swagger-typescript-client --additional-properties modelPropertyNaming=original,interface-only=true -DsupportingFiles -Dmodels

Steps to reproduce

Run swagger codegen for types with multiple refs

Reproduce the issue with the provided Docker command and a Swagger definition containing multiple allOf refs. Trace the typescript-aurelia generator's handling of those refs; done means the generated interface extends every referenced interface rather than only the first one, with a regression test covering the example.