Update dialyxir requirement from ~> 1.3.0 to ~> 1.4.0

Updates the requirements on [dialyxir](https://github.com/jeremyjh/dialyxir) to permit the latest version.
- [Release notes](https://github.com/jeremyjh/dialyxir/releases)
- [Changelog](https://github.com/jeremyjh/dialyxir/blob/master/CHANGELOG.md)
- [Commits](jeremyjh/dialyxir@1.3.0...1.4.0)

---
updated-dependencies:
- dependency-name: dialyxir
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

mix.exs

@@ -53,7 +53,7 @@ defmodule JSONAPI.Mixfile do
       {:earmark, ">= 0.0.0", only: :dev},
       {:credo, "~> 1.4", only: [:dev, :test], runtime: false},
       {:phoenix, "~> 1.3", only: :test},
-      {:dialyxir, "~> 1.3.0", only: [:dev, :test], runtime: false}
+      {:dialyxir, "~> 1.4.0", only: [:dev, :test], runtime: false}
     ]
   end