references for elixir and dynamo set.  erlang version info

To ensure dynamo and elixir work well at any given time specifying the git ref is important.

Two options for erlang version are

```ERL_CRASH_DUMP_SECONDS=0 erl -shutdown_time 1  -run 'exit(because)'```

And via elixir iex command -- ```iex --version``` -- 
which gives the version for both.