gpml:version ?

Browsing through the GPML RDF showed me the predicate 'gpml:version', which I actually cannot find in the original GPML ...? This relation could be removed in future versions, if irrelevant.

```SPARQL
<http://rdf.wikipathways.org/Pathway/WP4519_r119988>
gpml:version           "20161102" .
```