[BUG][Elm] use of pattern generates encoder that doesn't parse

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?

Description

Given the schema below, see that Elm generator has wrong behavior.

openapi-generator version

5.0.0 branch, 4th Feb 2020

OpenAPI declaration file content or url

    uuid4:
      type: string
      # Taken from https://stackoverflow.com/a/38191078/133235
      pattern: '^[0-9A-Fa-f]{8}-[0-9A-Fa-f]{4}-[4][0-9A-Fa-f]{3}-[89ABab][0-9A-Fa-f]{3}-[0-9A-Fa-f]{12}$'

Command line used for generation

openapi-generator-cli generate --input-spec openapi.yaml --enable-post-process-file --generator-name elm --config openapi-generator.yml --output openapi-client

Steps to reproduce

Generates encodeUuid4Pairs with a syntax error:

encodeUuid4 : Uuid4 -> Json.Encode.Value
encodeUuid4 =
    encodeObject << encodeUuid4Pairs


encodeUuid4WithTag : ( String, String ) -> Uuid4 -> Json.Encode.Value
encodeUuid4WithTag (tagField, tag) model =
    encodeObject (encodeUuid4Pairs model ++ [ encode tagField Json.Encode.string tag ])


encodeUuid4Pairs : Uuid4 -> List EncodedField
encodeUuid4Pairs model =
    let
        pairs =
            ]
    in
    pairs

cc @eriktim

Start by reproducing the issue with the supplied OpenAPI declaration and the openapi-generator-cli command using the elm generator. Inspect the generated encodeUuid4Pairs output and verify that the generated Elm is syntactically valid and can parse the pattern-based schema without the stray closing bracket.