replace .val to .once in jsbin of the docs/Graphs

[scenaristeur]

the new jsbin with .once instead of .val

https://jsbin.com/sebanirini/edit?js,console

to be updated in the line

Awesome, now run it all together: http://jsbin.com/webikepoxa/edit?js,console (Hit "Run", all logs except for the last one have been commented out).

of this page https://gun.eco/docs/Graphs