PDB-303 Utilise final version of prismatic/schema 0.2.0

Previously we were using our own published version of a pre 0.2.0 release, this
patch remedies that to now point at the upstream finalized version.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #795 from kbarber/ticket/1.6.x/PDB-303-utilise-final-version-of-schema-020

PDB-303 Utilise final version of prismatic/schema 0.2.0