Add missing dependency to mustache in opam file
Without this, opam does not install automatically "mustache", I had the following error message:
=-=- Processing actions -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
[ERROR] The compilation of logarion failed at "jbuilder build --root . -j 4 @install".
#=== ERROR while installing logarion.0.1 ======================================#
# opam-version 1.2.2
# os linux
# command jbuilder build --root . -j 4 @install
# path /home/cedlemo/.opam/system/build/logarion.0.1
# compiler system (4.05.0)
# exit-code 1
# env-file /home/cedlemo/.opam/system/build/logarion.0.1/logarion-28460-1872ec.env
# stdout-file /home/cedlemo/.opam/system/build/logarion.0.1/logarion-28460-1872ec.out
# stderr-file /home/cedlemo/.opam/system/build/logarion.0.1/logarion-28460-1872ec.err
### stderr ###
# Error: External library "mustache" not found.
# -> required by "src/converters/jbuild (context default)"
# Hint: try: jbuilder external-lib-deps --missing --root . @install