fix build script (edoc)

[clonejo]

Building was broken in R17:

make[1]: Leaving directory '/home/clonejo/code/mpdlog/deps/lager'
make[1]: Entering directory '/home/clonejo/code/mpdlog/deps/erlmpd'
(cd src;make)
make[2]: Entering directory '/home/clonejo/code/mpdlog/deps/erlmpd/src'
erl -noshell -run edoc file erlmpd.erl -run init stop
{"init terminating in do_boot",error}

edoc:file/1 is deprecated anyway, switching to edoc:files/1 fixes the problem.

[m7a]

@caolan: Does this patch have any chance of being included into the upstream? It works well for me and I have some follow-up patches that I would like to propose but from my point of view it would make sense to apply this one first?

[clonejo]

@m7a I mean, the library has seen (pretty much) no updates since 15 years :)