Use development version of InchEx

This is needed to avoid the following error:

```
(InchEx.Docs.Retriever.Error) module Mix.Tasks.Scenic.Hash was not compiled with flag --docs
```

Author: milmazz

mix.exs

@@ -99,7 +99,7 @@ defmodule Scenic.Mixfile do
       {:ex_doc, ">= 0.0.0", only: [:dev]},
       {:credo, ">= 0.0.0", only: [:dev, :test], runtime: false},
       {:excoveralls, ">= 0.0.0", only: :test, runtime: false},
-      {:inch_ex, ">= 0.0.0", only: :dev, runtime: false},
+      {:inch_ex, github: "rrrene/inch_ex", only: [:dev, :test], runtime: false},
       {:dialyxir, "~> 0.5", only: :dev, runtime: false}
     ]
   end