quick fix for windows compatibility

Hello,

I've been using this module on Windows, but I had to make a quick change first. Please deny with extreme prejudice if this has catastrophic effects that I haven't discovered yet.

Default behavior:
```
c:\>webpagetest -s http://localhost:9080 locations -d
{
  "url": "http://localhost:9080/\\getLocations.php"
}
c:\>webpagetest -s http://localhost:9080 locations
{
  "error": {
    "name": "WPTAPIError",
    "code": 400,
    "message": "Bad Request"
  }
}
```

New behavior:
```
c:\>webpagetest -s http://localhost:9080 locations -d
{
  "url": "http://localhost:9080/getLocations.php"
}
c:\>webpagetest -s http://localhost:9080 locations
{
  "response": {
    "statusCode": 200,
    "statusText": "Ok",
    "data": {
      "location": [
        {
...
```