Before, extensions were missing the definition of mandatory methods.
At the moment, it's not a problem because the coding guidelines are not
enforced by the code. But in the future, it will break.
Now, extensions have all mandatory method definitions.
When installed the extension will show there is an update available because this file says version `0.1` where the main [`extentions.json`](https://github.com/FreshRSS/Extensions/blob/master/extensions.json) shows version `0.2` is the latest which is inline with the extension README