[BUG] ip.isPrivate mocha test fail

# BUG
mocha test fail.
`ip.isPrivate` return wrong result.

# Repodruce
```sh
npm i ip@1.1.5
```

```js
ip=require('./node_modules/ip')
ip.isPrivate(ip.address('private', 'IPV6'))
```

# Expected
true

# Behavior
false

# Versions
Package version: 1.1.5
Runtime: nodejs v14.16.0 and v10.19.0 both fail.

Reproduce the failure with the issue's npm install and Node.js commands, then inspect the ip.isPrivate and ip.address entry points. Done means ip.isPrivate(ip.address('private', 'IPV6')) returns true on the reported Node.js versions, with the regression covered by an appropriate test.

Written by the indexing model from the issue text.