Add :crypto dependency to extra_applications

[vbaranov]

Adding :crypto dependency to extra_applications because of warning:

warning: :crypto.hash/2 defined in application :crypto is used by the current application but the current application does not depend on :crypto. To fix this, you must do one of:

  1. If :crypto is part of Erlang/Elixir, you must include it under :extra_applications inside "def application" in your mix.exs

  2. If :crypto is a dependency, make sure it is listed under "def deps" in your mix.exs

  3. In case you don't want to add a requirement to :crypto, you may optionally skip this warning by adding [xref: [exclude: [:crypto]]] to your "def project" in mix.exs

  lib/cid.ex:84: Cid.create_multihash/1

while integrating :cid package.

[nelsonic]

@vbaranov thanks for the addition. 🙏
Merging.
Follow-up task to publish new version: #57

[nelsonic]

@vbaranov Package published to https://hex.pm/packages/excid/1.0.2 📦 🚀 contains your change. Thanks again. 👌