Use canonical snapshot version 1.9.7-SNAPSHOT

Use canonical snapshot version 1.9.7-SNAPSHOT

Before, we used 1.9.7.BUILD-SNAPSHOT, which according to Andy Clement
was originally an intent across a group of Spring projects he was
involved in, to ensure that SNAPSHOTS were sorted alphabetically ahead
of MILESTONEs and ahead of RCs.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>