Update links in readme

Author: UX3D-kanzler

README.md

@@ -33,22 +33,22 @@ Features
 --------
 
 - [x] glTF 2.0
-- [x] [KHR_draco_mesh_compression](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_draco_mesh_compression)
-- [x] [KHR_lights_punctual](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_lights_punctual)
-- [x] [KHR_materials_clearcoat](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_clearcoat)
+- [x] [KHR_draco_mesh_compression](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_draco_mesh_compression)
+- [x] [KHR_lights_punctual](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_lights_punctual)
+- [x] [KHR_materials_clearcoat](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_clearcoat)
 - [x] [KHR_materials_emissive_strength](https://github.com/KhronosGroup/glTF/tree/KHR_materials_emissive_strength/extensions/2.0/Khronos/KHR_materials_emissive_strength)
-- [x] [KHR_materials_pbrSpecularGlossiness](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_pbrSpecularGlossiness)
-- [x] [KHR_materials_ior](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_ior)
-- [x] [KHR_materials_sheen](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_sheen)
-- [x] [KHR_materials_specular](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_specular)
-- [x] [KHR_materials_transmission](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_transmission)
-- [x] [KHR_materials_unlit](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit)
-- [x] [KHR_materials_variants](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_variants)
-- [x] [KHR_materials_volume](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_volume)
-- [x] [KHR_materials_iridescence](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_iridescence)
-- [x] [KHR_mesh_quantization](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_mesh_quantization)
-- [x] [KHR_texture_basisu](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_basisu)
-- [x] [KHR_texture_transform](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_transform)
+- [x] [KHR_materials_pbrSpecularGlossiness](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_pbrSpecularGlossiness)
+- [x] [KHR_materials_ior](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_ior)
+- [x] [KHR_materials_sheen](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_sheen)
+- [x] [KHR_materials_specular](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_specular)
+- [x] [KHR_materials_transmission](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_transmission)
+- [x] [KHR_materials_unlit](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_unlit)
+- [x] [KHR_materials_variants](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_variants)
+- [x] [KHR_materials_volume](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_volume)
+- [x] [KHR_materials_iridescence](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_iridescence)
+- [x] [KHR_mesh_quantization](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_mesh_quantization)
+- [x] [KHR_texture_basisu](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_texture_basisu)
+- [x] [KHR_texture_transform](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_texture_transform)
 - [x] [KHR_xmp_json_ld](https://github.com/KhronosGroup/glTF/pull/1893)