Try to fix installation script for OCaml 14.4 on Mac OSX

[acorrenson]

Hi there 👋

I tried to install coqffi (on Mac OSX) using the instructions in README.md but the command opam install . failed with the following message :

[ERROR] The compilation of coq-coqffi.dev failed at "./src-prepare.sh".

#=== ERROR while compiling coq-coqffi.dev =====================================#
# context     2.1.3 | macos/arm64 | ocaml.4.14.0 | pinned(git+file:///Users/arthur/Documents/github/coqffi#main#25448de5)
# path        ~/.opam/default/.opam-switch/build/coq-coqffi.dev
# command     ~/.opam/opam-init/hooks/sandbox.sh build ./src-prepare.sh
# exit-code   1
# env-file    ~/.opam/log/coq-coqffi-17538-14d9c1.env
# output-file ~/.opam/log/coq-coqffi-17538-14d9c1.out
### output ###
# sed: 1: "-": invalid command code -
# sed: 1: "-": invalid command code -
# unsupported OCaml version

After inspecting the script ./src-prepare.sh I realized the problem comes from the command sed - -e ... I could not find any documentation on the commande code - for sed but I realized that simply removing it solves the problem (and the CI still passes)...

If someone knows what is the problem I am very curious 😄 !

[lthms]

Looks like a typo on my end. Thanks for taking the time to submit this PR!