PHRAS-3934 fix videotools subtitle timeline #454

Job	Run time
build phraseanet-worker / build	4m 51s
build phraseanet-worker / build	4m 51s
build phraseanet-fpm / build	5m 19s
build phraseanet-fpm / build	5m 19s
build phraseanet-setup / build	4m 0s
build phraseanet-setup / build	4m 0s
build phraseanet-nginx / build	3m 34s
build phraseanet-nginx / build	3m 34s
build phraseanet-elasticsearch / build	39s
build phraseanet-elasticsearch / build	39s
build phraseanet-db / build	43s
build phraseanet-db / build	43s
unit test	4m 9s
unit test	15m 43s
	58m 4s

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