Remove legacy jsnext entry (reduxjs#2284)

Author: TrySound

package.json

@@ -4,7 +4,6 @@
   "description": "Predictable state container for JavaScript apps",
   "main": "lib/index.js",
   "module": "es/index.js",
-  "jsnext:main": "es/index.js",
   "typings": "./index.d.ts",
   "files": [
     "dist",