small change in docson.js that should fix the error

`docson.js` same fix as the branch `docson-hotfix`

In `vessels.json` I made a couple of changes for consistency: first, I've renamed `lat` and `lon` of the navigation object to `latitude` and `longitude`, as we're writing out everything else in full as well. Second, I've added some `property` blocks here and there with properties `self`, `timestamp` and `value`. It seemd weird that these properties didn't have them. 

Let me know what you guys think.