Mise à jour de 'Dockerfile'

Dockerfile

@@ -369,6 +369,9 @@ RUN dpkg --add-architecture i386 \
         /var/lib/apt/lists/* \
         /var/cache/apt/*
 
+# Keep APT package indexes available for Steam's dependency checker.
+RUN apt-get update \
+    && apt-get clean
 
 # =============================================================================
 # Runtime scripts