Add suport for Godot (gdscript)

**Name:** Godot 3 (gdscript)
**URL:** https://godotengine.org

Godot is a 2d/3d game engine. One of the primary languages is called gdscript, a language created specifically for the engine. Not sure if this is useful, but someone has already created a syntastic plugin, you can find it [here](https://github.com/clktmr/syntastic/commit/117b379ee8644bb5bc7545a29c6589bdd13cdcf9)