Update meck_cover for OTP 18.0
Update meck_cover for OTP 18.0

In order to avoid creating temporary files meck_cover needs direct
access to some unexported functions of cover.
In OTP 18.0 the internal API of cover changed a bit and
compile_beam/2 (which allows passing a binary instead just a filename)
was replaced by compile_beams/1.

See https://github.com/erlang/otp/commit/ab435488

kivra/meck,apache/couchdb-meck,basho/meck,soranoba/meck,edgurgel/meck,lilrooness/meck,eproxus/meck,norton/meck,ptuckey/meck