fix camera usage in example.
fix camera usage in example.

almarklein/visvis.dev,chrisidefix/visvis,pbfy0/visvis,Alwnikrotikz/visvis.dev,Alwnikrotikz/visvis,chiluf/visvis.dev,chrisidefix/visvis,pbfy0/visvis,Alwnikrotikz/visvis,pbfy0/visvis.dev,Alwnikrotikz/visvis,chrisidefix/visvis,AlanZatarain/visvis.dev,pbfy0/visvis