Upgrade Credo to version 0.6.0 (#201)

This merges a34861c into master.

.credo.exs

@@ -31,6 +31,7 @@
       {Credo.Check.Readability.ModuleNames},
       {Credo.Check.Readability.ParenthesesInCondition},
       {Credo.Check.Readability.PredicateFunctionNames},
+      {Credo.Check.Readability.Specs, false},
       {Credo.Check.Readability.TrailingBlankLine},
       {Credo.Check.Readability.TrailingWhiteSpace},
       {Credo.Check.Readability.VariableNames},

mix.exs

@@ -47,7 +47,7 @@ defmodule Thrift.Mixfile do
   defp deps do
      [{:ex_doc, "~> 0.14", only: :dev},
       {:excoveralls, "~> 0.6", only: [:dev, :test]},
-      {:credo, "~> 0.5", only: [:dev, :test]},
+      {:credo, "~> 0.6", only: [:dev, :test]},
       {:dialyxir, "~> 0.4", only: :dev, runtime: false}
      ]
   end

mix.lock

@@ -1,6 +1,6 @@
-%{"bunt": {:hex, :bunt, "0.1.6", "5d95a6882f73f3b9969fdfd1953798046664e6f77ec4e486e6fafc7caad97c6f", [], []},
+%{"bunt": {:hex, :bunt, "0.2.0", "951c6e801e8b1d2cbe58ebbd3e616a869061ddadcc4863d0a2182541acae9a38", [:mix], []},
   "certifi": {:hex, :certifi, "0.7.0", "861a57f3808f7eb0c2d1802afeaae0fa5de813b0df0979153cbafcd853ababaf", [:rebar3], []},
-  "credo": {:hex, :credo, "0.5.3", "0c405b36e7651245a8ed63c09e2d52c2e2b89b6d02b1570c4d611e0fcbecf4a2", [:mix], [{:bunt, "~> 0.1.6", [hex: :bunt, optional: false]}]},
+  "credo": {:hex, :credo, "0.6.0", "44a82f82b94eeb4ba6092c89b8a6730ca1a3291c7940739d5acc8806d25ac991", [:mix], [{:bunt, "~> 0.2.0", [hex: :bunt, optional: false]}]},
   "dialyxir": {:hex, :dialyxir, "0.4.1", "236056d6acd25f740f336756c0f3b5dd6e2f0156074bc15f3b779aeee15390c8", [:mix], []},
   "earmark": {:hex, :earmark, "1.0.3", "89bdbaf2aca8bbb5c97d8b3b55c5dd0cff517ecc78d417e87f1d0982e514557b", [:mix], []},
   "ex_doc": {:hex, :ex_doc, "0.14.5", "c0433c8117e948404d93ca69411dd575ec6be39b47802e81ca8d91017a0cf83c", [:mix], [{:earmark, "~> 1.0", [hex: :earmark, optional: false]}]},