Change About's URL from https://clusterrunner.com/ to https://www.clusterrunner.com/

Relates to https://github.com/box/ClusterRunner/issues/447

Please change https://github.com/box/ClusterRunner
> About:
>
> ClusterRunner makes it easy to parallelize test suites across your infrastructure in the fastest and most efficient way possible.
>
> [clusterrunner.com](https://clusterrunner.com/)

Specifically, change:
from:
> `[clusterrunner.com](https://clusterrunner.com/)`
to:
> `[clusterrunner.com](https://www.clusterrunner.com/)`

to prepend `www.` in front of `clusterunner`

to prevent Chrome from reporting the following:

**Steps to reproduce:**
1. Open Chrome
2. Go to https://github.com/box/ClusterRunner
3. In About, click https://clusterrunner.com/
4. The following error occurs:
```
Not Secure: https://clusterrunner.com/
```
```
Your connection is not private
Attackers might be trying to steal your information from clusterrunner.com (for example, passwords, messages, or credit cards). [Learn more](chrome-error://chromewebdata/#)
NET::ERR_CERT_COMMON_NAME_INVALID
```
```
This server could not prove that it is clusterrunner.com; its security certificate is from *.github.com. This may be caused by a misconfiguration or an attacker intercepting your connection.

[Proceed to clusterrunner.com (unsafe)](chro
me-error://chromewebdata/#)
```

**Whereas the expected outcome should be:**