[bugfix][Elm] Fix template when response schema is Map

Created by: matsubara0507

cc @eriktim

Generate wrong Elm code when response schema is Map (Dict).

e.g. generate from

openapi: 3.0.1
info:
  title: My title
  description: API under test
  version: 1.0.0
servers:
  - url: https://localhost:9999/root
paths:
  /dict1:
    get:
      responses:
        '200':
          description: 'return dictonary'
          content:
            application/json:
              schema:
                type: object
                additionalProperties:
                  type: boolean
  /dict2:
    get:
      responses:
        '200':
          description: 'return Object has dictionary'
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Hoge'
components:
  schemas:
    Hoge:
      type: object
      properties:
        hoge:
          type: object
          additionalProperties:
            type: boolean

to

dict1Get : Api.Request (Dict.Dict String Bool)
dict1Get =
    Api.request
        "GET"
        "/dict1"
        []
        []
        []
        Nothing
        (Json.Decode.dict Api.Data.boolDecoder)

dict2Get : Api.Request Api.Data.Hoge
dict2Get =
    Api.request
        "GET"
        "/dict2"
        []
        []
        []
        Nothing
        Api.Data.hogeDecoder

hogeDecoder : Json.Decode.Decoder Hoge
hogeDecoder =
    Json.Decode.succeed Hoge
        |> maybeDecode "hoge" (Json.Decode.dict Json.Decode.boolboolDecoder) Nothing

but expected

dict1Get : Api.Request (Dict.Dict String Bool)
dict1Get =
    Api.request
        "GET"
        "/dict1"
        []
        []
        []
        Nothing
        (Json.Decode.dict Json.Decode.bool)

dict2Get : Api.Request Api.Data.Hoge
dict2Get =
    Api.request
        "GET"
        "/dict2"
        []
        []
        []
        Nothing
        Api.Data.hogeDecoder

hogeDecoder : Json.Decode.Decoder Hoge
hogeDecoder =
    Json.Decode.succeed Hoge
        |> maybeDecode "hoge" (Json.Decode.dict Json.Decode.bool) Nothing

fix it

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