Create ci.json (#283)

Add codesandbox CI to all pull requests

Author: thebuilder

.codesandbox/ci.json

@@ -0,0 +1,6 @@
+{
+  "sandboxes": ["react-intersection-observer-ud2vo"],
+  "publishDirectory": {
+    "react-intersection-observer": "dist"
+  }
+}