Intermittent slideshare failure

This is occasionally tripping up the build
```
[2014-05-27T07:26:11.094Z] ERROR: oae-preview-processor/9244 on testing-worker-linux-8-2-12220-linux-3-26104701: Failed to interact with the SlideShare API
    err: {
      "Message": [
        {
          "_": "You must use https:// to access this API endpoint",
          "$": {
            "ID": "24"
          }
        }
      ]
    }
```
We can probably notate this as a constant: `SLIDESHARE_API_URL`