Missing dependency on ppx_deriving_cmdliner

[tavinathanson]

epidisco installation fails because of a missing ppx_deriving_cmdliner dependency:

From @smondet: https://github.com/hammerlab/epidisco/blob/master/opam/opam#L14-L20

Processing  1/1: [epidisco: omake uninstall]
#=== ERROR while installing epidisco.0.0.0+master =============================#
# opam-version 1.2.2
# os           linux
# command      omake
# path         /home/tavi/.opam/4.03.0/build/epidisco.0.0.0+master
# compiler     4.03.0
# exit-code    2
# env-file     /home/tavi/.opam/4.03.0/build/epidisco.0.0.0+master/epidisco-3875-a71bb4.env
# stdout-file  /home/tavi/.opam/4.03.0/build/epidisco.0.0.0+master/epidisco-3875-a71bb4.out
# stderr-file  /home/tavi/.opam/4.03.0/build/epidisco.0.0.0+master/epidisco-3875-a71bb4.err
### stdout ###
# LIB epidisco MODULES: tool_configuration qc pipeline parameters save_result command_line final_report extended_edsl metadata
# [...]
#       DEPS:
#       INCLUDES: .
# *** omake: finished reading OMakefiles (0.04 sec)
# --- Checking if ocamldep understands -modules... (yes)
# - scan _build/src/lib scan-ocaml-final_report.ml
# + ocamlfind ocamldep -package biokepi,ppx_deriving.std,ppx_deriving_cmdliner -modules final_report.ml
#      | Shell.ocamldep-postproc()
# *** omake: 12/77 targets are up to date
# *** omake: failed (0.05 sec, 1/1 scans, 0/0 rules, 22/80 digests)
### stderr ###
# ocamlfind: Package `ppx_deriving_cmdliner' not found
# *** omake: targets were not rebuilt because of errors:
#    <scanner _build/src/lib/scan-ocaml-final_report.ml>
#       depends on: _build/src/lib/final_report.ml```

[smondet]

This has been fixed.