Release Note: Change default GC to G1

In JDK 9, the default garbage collector is G1 when a garbage collector is not explicitly specified. G1 provides a better overall experience for most users when compared to a throughput-oriented collector such as the Parallel GC, which was previously the default.

The options to configure the G1 collector are documented in the java command page ([`link`](http://www.oracle.com/pls/topic/lookup?ctx=javase9&id=JSWOR624)). See also [JEP 248](http://openjdk.java.net/jeps/248) for more information on this change.