chore(Elixir): Fix charlist warning in elixir 1.17

[tomciopp]

@riverrun Elixir emits a warning for charlists not declared using the ~c"" sigil in version 1.17.0. Looking up the docs for erlang's filename module it looks like strings are the preferred method for joining paths.

https://www.erlang.org/doc/apps/stdlib/filename.html#join/1