V3 compatible only 8.9.0 and more

#### Issue Description
On package.json it say 
```
"engines": {
    "node": ">= 7.6.0",
    "npm": ">= 3.10.0"
  },
```

But dependency joi is in version 13 witch is compatible node >=8.9.0. if you use yarn as package manager it just crash on node <8.9.0 

Trails version: 3.0.3 => master say 3.1.0 and doesn't have joi anymore 