The forge version references to the  4.3.3 version of the plugin(https://github.com/apache/cordova-plugin-file.git#4.3.3). If you go to the github repository and check its tags, you can pick a version. From what i see 6.0.2 is the latest version. You also have to keep in mind that some methods might have been deprecated and new ones added and some extra work might have to be done.