fix docker ci master #598

Job	Run time
coq	1m 15s
stdlib	1m 9s
coq-elpi	1m 39s
hierarchy-builder	1m 29s
mathcomp-ssreflect	3m 11s
mathcomp-bigenough	1m 26s
mathcomp-finmap	1m 46s
mathcomp-fingroup	2m 2s
mathcomp-algebra	3m 33s
mathcomp-solvable	2m 56s
mathcomp-classical	2m 47s
multinomials	2m 14s
mathcomp-reals	2m 22s
mathcomp-field	4m 31s
mathcomp-reals-stdlib	1m 47s
mathcomp-experimental-reals	2m 1s
mathcomp-character	2m 41s
mathcomp-analysis	9m 29s
mathcomp-real-closed	2m 44s
mathcomp	1m 54s
odd-order	17m 8s
mathcomp-analysis-stdlib	13m 8s
	1h 23m 12s

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