Java-cf-env v3.1.3: upgrade dependency, fix DB2 url properties

Get it while it's hot!

<dependency>
	<groupId>io.pivotal.cfenv</groupId>
	<artifactId>java-cfenv-boot</artifactId>
	<version>3.1.3</version>
</dependency>

What's Changed

This new release uses the latest json-io, version 4.15.0, and fixes an issue with DB2 connection properties, see #234

Thanks to @Marty850 for creating the DB2 issue #231 !

Enjoy!