fix deprecation warning for File.iterator! -> File.stream!

Fixes the following deprecation warnings when running the tests

```
[WARNING] File.iterator!/2 is deprecated, please use File.stream!/2 instead
    /Users/reset/code/elixir/lib/elixir/lib/file.ex:972: File.iterator!/2
    /Users/reset/code/dynamo/lib/dynamo/filters/exceptions/debug.ex:128: Dynamo.Filters.Exceptions.Debug.extract_snippet/2
    /Users/reset/code/dynamo/lib/dynamo/filters/exceptions/debug.ex:111: Dynamo.Filters.Exceptions.Debug.file_context/4
    /Users/reset/code/dynamo/lib/dynamo/filters/exceptions/debug.ex:63: Dynamo.Filters.Exceptions.Debug.each_frame/5
    /Users/reset/code/elixir/lib/elixir/lib/enum.ex:686: Enum."-map_reduce/3-fun-0-"/3
    /Users/reset/code/elixir/lib/elixir/lib/enum.ex:1518: Enumerable.List.reduce/3
    /Users/reset/code/elixir/lib/elixir/lib/enum.ex:685: Enum.map_reduce/3
```