script tag in index.html incorrect when using full url as baseurl

**I'm submitting a bug report**

* **Library Version:**
0.32.3

**Please tell us about your environment:**
* **Operating System:**
Windows 10

* **Language:**
all

**Current behavior:**
When you configure the baseUrl to be a full url in aurelia.json, the CLI will patch index.html. But the script tag ends up being incorrect:

``

note the single slash after `http:`

This happens because of [path.posix.join](https://github.com/aurelia/cli/blob/master/lib/build/bundle.js#L231).

**Expected/desired behavior:**
There to be two slashes after `http:`

* **What is the motivation / use case for changing the behavior?**
Being able to use a full URL as baseurl, so hosting the bundles on a different server than the server that's serving the index file