Update public_suffix to ~> 1.4.2

The latest `public_suffix` release has better support for new gTLDs.

For example, on `master`:
```
> PostRank::URI.valid?('http://en.trademarks.directory')
=> false
```

but with this patch, `.directory` (and many others) are added as valid gTLDs:
```
> PostRank::URI.valid?('http://en.trademarks.directory')
=> true
```