Architecture bug

IEDriverServer is downloaded for wrong architecture.

IEDriverServer_x64_2.39.0.zip is downloaded for Win32 which results in:
```
$ dalek test-script.js -b IE
Running tests
>> ERROR: Error: spawn Unknown system errno 216
```

IEDriverServer_Win32_2.39.0 works, however, fine in 64-bit windows.

I also updated the driver version to 2.40.

Keep up the good work! DalekJS rocks!