Fixed port number detection to be more precise

The detection of the port 8021 would be falsely detected if ports containing "8021" were open, such as 18021 or 80219. An example of false detection is in the below screenshot:

![port](https://cloud.githubusercontent.com/assets/419731/5060083/199c8016-6d0b-11e4-9955-1015ae0fdbb3.png)


The code in this pull request works on my machine, to more properly detect port 8021 using a simple regex.