Error: command plug is breaking by node 8
I can't execute branch 1.6 (commit https://git.duniter.org/nodes/typescript/duniter/commit/9989856c764e28f357242d63e6a9bd0002081897) after use the `plug` command
```
$ bin/duniter direct_start
module.js:538
throw err;
^
Error: Cannot find module 'co'
at Function.Module._resolveFilename (module.js:536:15)
at Function.Module._load (module.js:466:25)
at Module.require (module.js:579:17)
at require (internal/module.js:11:18)
at Object.<anonymous> (/home/elois/dev/duniter/bin/duniter:4:12)
at Module._compile (module.js:635:30)
at Object.Module._extensions..js (module.js:646:10)
at Module.load (module.js:554:32)
at tryModuleLoad (module.js:497:12)
at Function.Module._load (module.js:489:3)
```
issue