Replace sandbox

Author: vanruesc

.github/ISSUE_TEMPLATE/bug_report.md

@@ -13,7 +13,7 @@ A clear and concise description of what the bug is.
 
 ### To Reproduce
 
-Describe the steps to reproduce the behavior and provide a minimal example that demonstrates the issue. You can use the demo sandbox as a starting point: https://codesandbox.io/s/postprocessing-25rts
+Describe the steps to reproduce the behavior and provide a minimal example that demonstrates the issue. You can use the demo sandbox as a starting point: https://stackblitz.com/edit/postprocessing-v6
 
 
 ### Expected behavior

README.md

@@ -5,7 +5,7 @@
 
 A post processing library for [three.js](https://threejs.org/).
 
-*[Demo](https://pmndrs.github.io/postprocessing/public/demo) · [Sandbox](https://codesandbox.io/s/postprocessing-25rts) · [Documentation](https://pmndrs.github.io/postprocessing/public/docs) · [Wiki](https://github.com/pmndrs/postprocessing/wiki)*
+*[Demo](https://pmndrs.github.io/postprocessing/public/demo) · [Sandbox](https://stackblitz.com/edit/postprocessing-v6) · [Documentation](https://pmndrs.github.io/postprocessing/public/docs) · [Wiki](https://github.com/pmndrs/postprocessing/wiki)*
 
 ## Installation