Change binary_to_list for String.to_char_list!

Elixir v0.10.2 deprecated binary_to_list:

https://github.com/elixir-lang/elixir/blob/v0.10.2/CHANGELOG.md#v0102-2013-09-03

```
binary_to_list/1 is deprecated. Please use String.to_char_list!/1
instead unless you are working with bytes, then you should use
:binary.bin_to_list/
```