Fixes to scala-gatling generated scripts

[drairi]

PR checklist

• ✅ 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.
• ❌ Copied the technical committee to review the pull request if your PR is targeting a particular programming language. (there isn't one for Scala) 😞

Description of the PR

• There was a mistake in the authorizationHeader - it didn't match the default one in the conf files
• baseURL should be baseUrl
• Fetch config files from the right place.

[frantuma]

Thanks!