fix: adjust gettext usage

The new version of [`Gettext`][0] changed the way it's used, to avoid
large penalties when recompiling large projects.

[0]: https://github.com/elixir-gettext/gettext/blob/main/CHANGELOG.md#v0260

lib/wabanex_web/gettext.ex

@@ -5,7 +5,7 @@ defmodule WabanexWeb.Gettext do
   By using [Gettext](https://hexdocs.pm/gettext),
   your module gains a set of macros for translations, for example:
 
-      import WabanexWeb.Gettext
+      use Gettext, backend: WabanexWeb.Gettext
 
       # Simple translation
       gettext("Here is the string to translate")
@@ -20,5 +20,5 @@ defmodule WabanexWeb.Gettext do
 
   See the [Gettext Docs](https://hexdocs.pm/gettext) for detailed usage.
   """
-  use Gettext, otp_app: :wabanex
+  use Gettext.Backend, otp_app: :wabanex
 end