Disabled Data functionality
When adding `require('sketch/dom').getSelectedDocument()` to the code of a Data Plugin, the Data Plugin part of that plugin gets disabled (through Sketch) without the possibility to enable it again (through the user).

Environment: Sketch Version 54, Mac OS Mojave (v. 10.14.3)
How to reproduce:

1. Create a Sketch Data Plugin 
2. Add the code `let document = require('sketch/dom').getSelectedDocument()` to the data related JS file.
3. Build the plugin
4. Open Sketch
5. Go to `Sketch` > `Preferences` > `Data` and scroll to the specific Data Plugin line - the plugin is disbaled (see screenshot attached).
![Bildschirmfoto 2019-04-10 um 10 42 51](https://user-images.githubusercontent.com/5039952/55864905-a80d6300-5b7d-11e9-979e-0c8d339b1fa6.png)

