Add :excoveralls package and config

mix.exs

@@ -13,7 +13,13 @@ defmodule GiphyEx.Mixfile do
       deps: deps(),
       docs: [
         main: "GiphyEx"
-      ]
+      ],
+      preferred_cli_env: [
+        "coveralls": :test,
+        "coveralls.html": :test,
+        "coveralls.json": :test,
+      ],
+      test_coverage: [tool: ExCoveralls]
     ]
   end
 
@@ -28,8 +34,9 @@ defmodule GiphyEx.Mixfile do
     [
       { :earmark, "~> 0.1", only: :dev },
       { :ex_doc, "~> 0.11", only: :dev },
-      { :exjsx, "~> 3.2.0", app: false },
-      { :httpoison, "~> 0.6" }
+      { :exjsx, "~> 3.2.0", app: false, override: true },
+      { :httpoison, "~> 0.6" },
+      { :excoveralls, "~> 0.5.7", only: :test }
     ]
   end
 

mix.lock

@@ -1,6 +1,7 @@
 %{"certifi": {:hex, :certifi, "0.7.0", "861a57f3808f7eb0c2d1802afeaae0fa5de813b0df0979153cbafcd853ababaf", [:rebar3], []},
   "earmark": {:hex, :earmark, "0.2.1", "ba6d26ceb16106d069b289df66751734802777a3cbb6787026dd800ffeb850f3", [:mix], []},
   "ex_doc": {:hex, :ex_doc, "0.12.0", "b774aabfede4af31c0301aece12371cbd25995a21bb3d71d66f5c2fe074c603f", [:mix], [{:earmark, "~> 0.2", [hex: :earmark, optional: false]}]},
+  "excoveralls": {:hex, :excoveralls, "0.5.7", "5d26e4a7cdf08294217594a1b0643636accc2ad30e984d62f1d166f70629ff50", [:mix], [{:exjsx, "~> 3.0", [hex: :exjsx, optional: false]}, {:hackney, ">= 0.12.0", [hex: :hackney, optional: false]}]},
   "exjsx": {:hex, :exjsx, "3.2.1", "1bc5bf1e4fd249104178f0885030bcd75a4526f4d2a1e976f4b428d347614f0f", [:mix], [{:jsx, "~> 2.8.0", [hex: :jsx, optional: false]}]},
   "hackney": {:hex, :hackney, "1.6.3", "d489d7ca2d4323e307bedc4bfe684323a7bf773ecfd77938f3ee8074e488e140", [:mix, :rebar3], [{:certifi, "0.7.0", [hex: :certifi, optional: false]}, {:idna, "1.2.0", [hex: :idna, optional: false]}, {:metrics, "1.0.1", [hex: :metrics, optional: false]}, {:mimerl, "1.0.2", [hex: :mimerl, optional: false]}, {:ssl_verify_fun, "1.1.1", [hex: :ssl_verify_fun, optional: false]}]},
   "httpoison": {:hex, :httpoison, "0.10.0", "4727b3a5e57e9a4ff168a3c2883e20f1208103a41bccc4754f15a9366f49b676", [:mix], [{:hackney, "~> 1.6.3", [hex: :hackney, optional: false]}]},