PHRAS-3934 fix videotools subtitle timeline #458

Job	Run time
build phraseanet-worker / build	5m 17s
build phraseanet-nginx / build	3m 9s
build phraseanet-setup / build	5m 13s
build phraseanet-fpm / build	5m 34s
build phraseanet-db / build	35s
build phraseanet-elasticsearch / build	23s
unit test	12m 11s
	32m 22s

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