Credo fixes to comply with --strict option (#177)

* Credo fixes to comply with --strict option

* Add --strict option to mix credo on Travis

.travis.yml

@@ -39,6 +39,6 @@ cache:
 
 script:
   - mix test
-  - mix credo
+  - mix credo --strict
   - if [[ `elixir -v` = *"1.8"* ]]; then mix dialyzer --halt-exit-status; fi
   - if ! [[ `elixir -v` = *"1.5"* ]]; then mix format --check-formatted; fi

lib/jsonapi.ex

@@ -9,7 +9,7 @@ defmodule JSONAPI do
   in your `config/config.exs`:
       config :jsonapi, :json_library, Jason
   """
-  def json_library() do
+  def json_library do
     module = Application.get_env(:jsonapi, :json_library, Jason)
 
     if Code.ensure_loaded?(module) do
@@ -30,7 +30,5 @@ defmodule JSONAPI do
   @doc """
   This returns the MIME type for JSONAPIs
   """
-  def mime_type() do
-    @mime_type
-  end
+  def mime_type, do: @mime_type
 end

lib/jsonapi/serializer.ex

@@ -5,8 +5,8 @@ defmodule JSONAPI.Serializer do
 
   import JSONAPI.Ecto, only: [assoc_loaded?: 1]
 
-  alias JSONAPI.Utils.String, as: JString
-  alias JSONAPI.Config
+  alias JSONAPI.{Config, Utils}
+  alias Utils.String, as: JString
 
   require Logger