Adding 'no-cache-dir' extra argumuments

Perhaps using no-cache-dir will preview out-of-memory errors on
Raspberry Pi.

Fixes #908

roles/kolibri/tasks/main.yml

@@ -23,6 +23,7 @@
   pip:
     name: kolibri
     state: latest
+    extra_args: --no-cache-dir
   when: internet_available
 
 - name: Create kolibri systemd service file