fix: Empty body convert in Hash on GET requests

[Vitor-Novaes]

Problem:

When GET routes called in Asaas::Api::Base.list method, body nil convert to Hash and become json body data, causing 403 error status CloudFront response

Solution Add method parser body to keep body nil when request method doenst have it, prevent sending empty hash

[marcosgugs]

Great job @Vitor-Novaes