Fix ordering issue of ZeroMQ path discovery

There is issue in ZeroMQ library path discovery process.

The `map` method goes **before**  `+` of between `Arrays`. 

So we have no chance to load `ZeroMQ` shared library from a lot of places.

ZMQ_LIB_PATHS (after `+` and `map`)
```ruby
["/opt/boxen/rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/ffi-rzmq-1.0.2/lib/ffi-rzmq/../../ext",
 "/opt/boxen/rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/bin",
 "/opt/boxen/rbenv/versions/2.0.0-p247/bin",
 "/opt/boxen/rbenv/libexec",
 "/opt/boxen/rbenv/plugins/ruby-build/bin",
 "bin",
 "/opt/boxen/rbenv/shims",
 "/opt/boxen/rbenv/bin",
 "/opt/boxen/bin",
 "/opt/boxen/homebrew/bin",
 "/opt/boxen/homebrew/sbin",
 "/usr/bin",
 "/bin",
 "/usr/sbin",
 "/sbin",
 "/usr/local/bin",
 "/opt/X11/bin",
 "/usr/texbin",
 "/usr/local/lib/libzmq.dylib",
 "/opt/local/lib/libzmq.dylib",
 "/usr/local/homebrew/lib/libzmq.dylib",
 "/usr/lib64/libzmq.dylib"]
```