Fixed #45 that ResourceBundle.Control is not supported in named modules

[kasecato]

You can't use ResourceBundle.Control if you're using modules with JDK 9 or later. This library does not support JDK 9, so I can't write test code, sorry.

ResourceBundle.Control is not supported in named modules. If the getBundle method with a ResourceBundle.Control is called in a named module, the method will throw an UnsupportedOperationException
https://docs.oracle.com/javase/9/docs/api/java/util/ResourceBundle.html#bundleprovider

[vvatanabe]

@kasecato Thank you for the great PR. LGTM ;D