Remove spindle of serendipity as it's not open source

This closes #153.

README.md

@@ -52,7 +52,6 @@ See [Vivraan/godot-lang-support](https://github.com/Vivraan/godot-lang-support).
 - [Platshoot](https://github.com/Calinou/platshoot) - A 2D shooter game (Godot 2.1).
 - [Ringed](https://github.com/KOBUGE-Incubator/ringed) - Top-down shooter with extensive usage of light effects (Godot 2.1).
 - [SealedBite](https://github.com/securas/SealedBite) - 2D platformer game, winner of the GitHub Game Off 2019 jam (Godot 3.1).
-- [spindle of serendipity](https://zacryol.itch.io/spindle-of-serendipity) - Word guessing game with customizable entries (Godot 3.2).
 - [SuperStarfighter](https://github.com/notapixelstudio/superstarfighter) - Fast-paced local party game with starships that battle in a top-down arena (Godot 3.1).
 - [Tanks of Freedom](https://github.com/w84death/Tanks-of-Freedom) - Free turn-based isometric strategy game (Godot 2.1).
 - [Three Hungry Mice](https://github.com/delstuff/threeHungryMice) - Breakout game with mice made for the Godot Engine Jam of March 2016 (Godot 2.1).