Add main (e.g. so that https://unpkg.com/three.interactive resolves properly)

Author: markuslerner

package.json

@@ -1,9 +1,10 @@
 {
   "name": "three.interactive",
-  "version": "1.3.0",
+  "version": "1.3.1",
   "description": "Fast and simple interaction manager for THREE.js",
   "type": "module",
   "types": "./build/index.d.ts",
+  "main": "./build/three.interactive.js",
   "module": "./build/three.interactive.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",