Use Java 8 idioms

[brownian-motion]

This PR improves the readability of the Java code used in this example by adopting idioms introduced in Java 8 and earlier.

These changes intend to make the intent and behavior of the code more visible by reducing the amount of boilerplate code.

This change also updates various dependencies to the latest compatible minor version, in order to fix the build process on Java 8+ JDKs.