fix for builder.Url.hostname regex

Quick fix to the builder.Url.hostname regex.

Pre-change behavior:
```
>>> new builder.Url('http://www.shopping.hp.com/en_US/home-office/-/products/Laptops/Laptops').hostname();
"http://www.shopping.hp.com/en_US/home-office/-/products/Laptops/Laptops"
```
Post-change behavior:
```
>>> new builder.Url('http://www.shopping.hp.com/en_US/home-office/-/products/Laptops/Laptops').hostname();
"www.shopping.hp.com"
```