When building using Java, read files as UTF-8

When building on windows using Rhino (like RequireJS plugin with maven), the encoding of the files was wrong. FileReader reads a file using the system's default encoding.

This might be something that should be configurable, but the RequireJS-docs says that files should be in Unicode, so I'm thinking this is fine.

Concerning tests, I'm not sure if testing the the Java-side is relevant here?