fix default CMD of nextcloud container #93

Job	Run time
Build App Containers (etherpad) / Build etherpad	42s
Build App Containers (limesurvey) / Build limesurvey	1m 12s
Build App Containers (minecraft) / Build minecraft	22s
Build App Containers (indico) / Build indico	2m 10s
Build App Containers (nextcloud) / Build nextcloud	1m 30s
Build App Containers (sogo) / Build sogo	2m 44s
	8m 40s

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