Fixed InstallOptions' URL building

Hi,

Installing jar as a process seems to be broken in the latest Fabric. One of the problems I've encoutered is related to the `NullPointerException` being thrown during the jar installation process.

The reason behind the mentioned NPE is the fact that `InstallOptionsBuilder` doesn't calculate URL of the artifact being installed when creating new `InstallOptions` instance. Builder reads the value of `url` field, while it should call `getUrl()` method instead.

I've fixed the issue and attached appropriate unit test.

Cheers.

PS There are some other issues related to the installation of jar via process manager - I'll commit appropriate fixes in the next pull requests.