Fix URIBuilder groovy example

The .with closure returns the last result, not the object.

Old example:

    groovy> import groovyx.net.http.URIBuilder
    groovy> new URIBuilder('http://www.google.com/').with {
    groovy>     scheme = 'https'
    groovy>     port = 443
    groovy>     path = 'some/path'
    groovy>     query = [p1:1, p2:'two']
    groovy> }
    
    ["p1":1, "p2":"two"]

New example:

    groovy> new URIBuilder('http://www.google.com/').with {
    groovy>     scheme = 'https'
    groovy>     port = 443
    groovy>     path = 'some/path'
    groovy>     query = [p1:1, p2:'two']
    groovy>     return it
    groovy> }

    https://www.google.com:443/some/path?p1=1&p2=two