Update version from 1.3-SNAPSHOT to 1.3.1-SNAPSHOT.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/exec/trunk@1637095 13f79535-47bb-0310-9956-ffa450edef68
Add version 1.3.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/exec/trunk@1637096 13f79535-47bb-0310-9956-ffa450edef68