Issue 6754: Change version on master branch to 0.13 (#6755)
Issue 6754: Change version on master branch to 0.13 (#6755)

As r0.12 has been created, upgrade Pravega version in gradle.properties to 0.13.0-SNAPSHOT.

Signed-off-by: Raúl Gracia <7174a4413a205e30b13c6260874593a5bb32ef52@emc.com>
pravega/pravega,pravega/pravega,pravega/pravega