update Makefile

4 jobs for master in 5 minutes and 43 seconds (queued for 15 seconds)
Status Name Job ID Coverage
  Build
passed stdpp-coq8.6 #3494
fp-timing

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passed stdpp-coq8.6.1 #3493
fp-timing

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passed stdpp-coq8.7 #3492
fp-timing

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  Opam
passed opam #3495

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