Fixed problem with browser list.

Original problem if we put spaces after comma in the browser list the plugin is not generating the karma command correctly.
e.g in ```configuration``` if we do 
```
<browsers>PhantomJS, Chrome</browsers>
```
The plugin is not generating the karma process command correctly, and because of that the test on `Chrome` browser is not getting executed and all we see is just a `warning`.
The code fix check for spaces after the comma in the `browsers` list and appropriately construct the correct browser list.