fix issue with intersection-demo.json

[kfarr]

fix issue with intersection-demo.json

to reproduce:

• use editor repo
• go to http://localhost:3333/index-mapbox-intersection.html
• save as 3dstreet json (that is how the file referenced above was made)
• reopen in 3dstreet viewer, then load the saved scene
• then click load 3dstreet editor to inspect the scene
• notice that there are some cars out of place and there are 2 street parents where there should only be 1 street

[Algorush]

PR to fix: #321
I'll also add this fixings to 3dstreet-editor

[kfarr]

closed by #321