Fixed plugin dir path for java

[naveed-ahmad]

I'm quite new to cordova, so not sure how to make this backward compatible. But..looks like java src directory is changed in cordova 8.0.

I got this exception:

UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: ENOENT: no such file or directory, open 'path-to-project/platforms/android/src/com/qhng/cordova/DecryptResourceNG.java'
(node:41796) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Fixed that by updating the plugin directory path.