[Elm] Fix elm format in Byte.mustache

[andys8]

PR checklist

• [x] Read the contribution guidelines.
• [ ] Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• [ ] Filed the PR against the correct branch: 3.0.0 branch for changes related to OpenAPI spec 3.0. Default: master.
• [x] Copied the technical committee to review the pull request if your PR is targeting a particular programming language. (There is nobody)

Description of the PR

I created a minor fix. The format in the file did not match the defacto standard of elm-format. I changed it and want to get into the implementation.

[eriktim]

Thanks @andys8, LGTM

cc: @wing328