[Ninjabot] NinjaBot requires dateutil

Signed-off-by: Yohann D'ANELLO <ynerant@crans.org>

roles/ninjabot/tasks/main.yml

 ---
-- name: Install python3 IRC library
+- name: Install Ninjabot dependencies
   apt:
-    name: python3-irc
-    state: present
-    update_cache: true
-  register: apt_result
-  retries: 3
-  until: apt_result is succeeded
-
-- name: Install Flask for python3
-  apt:
-    name: python3-flask
+    name:
+      - python3-dateutil
+      - python3-flask
+      - python3-irc
     state: present
     update_cache: true
   register: apt_result