add parentheses to module metadata function calls

[tfiedlerdejanze]

The elixir 1.17.3 compiler prints a warning for these:

warning: using map.field notation (without parentheses) to invoke function MySerializer.__attributes() is deprecated, you must add parentheses instead: remote.function()
  (remodel 0.0.4) lib/remodel/formatters/map_formatter.ex:14: Remodel.Formatter.MapFormatter.format_resource/3
  (remodel 0.0.4) lib/remodel/formatters/map_formatter.ex:3: Remodel.Formatter.MapFormatter.format/3