Could not load config config/dev.secret.exs

[charleshan]

The problem starts from Chapter 11: OTP (otp/listings/rumbl/mix.change1.exs)

$ mix deps.get
** (Mix.Config.LoadError) could not load config config/dev.secret.exs
    ** (Code.LoadError) could not load /Users/User/Documents/Programming/elixir/programming_phoenix/rumbl/config/dev.secret.exs
    (elixir) lib/code.ex:657: Code.find_file/2
    (elixir) lib/code.ex:295: Code.eval_file/2
    (mix) lib/mix/config.ex:161: Mix.Config.read!/1
    (mix) lib/mix/config.ex:195: anonymous fn/2 in Mix.Config.read_wildcard!/1
    (elixir) lib/enum.ex:1623: Enum."-reduce/3-lists^foldl/2-0-"/3
    (stdlib) erl_eval.erl:670: :erl_eval.do_apply/6
    (stdlib) erl_eval.erl:878: :erl_eval.expr_list/6
    (stdlib) erl_eval.erl:404: :erl_eval.expr/5

The project follows the convention of using .gitignore to exclude secrets from git. This means that we set up the configuration file using a API key from Wolfram Alpha Developer Portal. Maybe we can include the secret.exs for the sake of simplicity.