docs(readme): update features checkboxes (#49)

Author: xhudec

README.md

@@ -38,7 +38,7 @@
 - [x] Fully typed with TypeScript
 - [x] Based on [our already existing open source tools](https://www.strv.io/tools/frontend)
   - [`code-quality-tools`](https://github.com/strvcom/code-quality-tools)
-- [ ] **WIP** Properly tested
+- [x] Properly tested
 
 ## Install