[meta] add sideEffects flag

Author: ljharb

package.json

@@ -7,6 +7,7 @@
 ".": "./index.js",
 "./package.json": "./package.json"
 },
+"sideEffects": false,
 "scripts": {
 "prepack": "npmignore --auto --commentLines=autogenerated",
 "prepublishOnly": "safe-publish-latest",