update Makefile

1 job for master in 15 minutes and 27 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #48115
fp
build-iris.dev

00:15:27

 
Name Stage Failure
failed
build-iris.dev Build
| - remove coq-stdpp         dev
| - remove num 1.2
+-

The former state can be restored with:
opam switch import "/builds/iris/iron/opamroot/ocaml-base-compiler.4.07.1/.opam-switch/backup/state-20191121013428.export"
Or you can retry to install your package selection with:
opam install --restore
ERROR: Job failed: exit code 1