Read variable for testing db.

config/test.exs

@@ -18,7 +18,7 @@ config :pleroma, Pleroma.Repo,
   username: "postgres",
   password: "postgres",
   database: "pleroma_test",
-  hostname: "localhost",
+  hostname: System.get_env("DB_HOST") || "localhost",
   pool: Ecto.Adapters.SQL.Sandbox