fix: use correct es5 entry point

Author: pimlie

package.json

@@ -2,7 +2,7 @@
   "name": "tib",
   "version": "0.5.0",
   "description": "Easy e2e browser testing in Node",
-  "main": "lib/index.js",
+  "main": "lib/tib.js",
   "module": "src/index.js",
   "repository": "https://github.com/pimlie/tib",
   "author": "pimlie <pimlie@hotmail.com>",