Julia 0.6 support

[femtotrader]

Hello,

Running tests raise an exception with Julia 0.6

$ julia test/runtests.jl
ERROR: LoadError: LoadError: UndefVarError: @unix_only not defined
Stacktrace:
 [1] include_from_node1(::String) at ./loading.jl:569
while loading /Users/femto/.julia/v0.6/Zlib/src/Zlib.jl, in expression starting on line 28
while loading /Users/femto/.julia/v0.6/Zlib/test/runtests.jl, in expression starting on line 2

Kind regards