Switching to ES5 instead of ES6 standard in the NFT examples

[kalwalt]

As pointed in this comment #1 (comment) we should switch to ES5 standard.
If you find other code that use ES6 standard please leave me a note here.

[nicolocarpignoli]

done with 2103d75

if it's ok for you we can close this one :)

[kalwalt]

@nicolocarpignoli only one last thing: i commented in the code and after it is ok.

[kalwalt]

Perfect! we can close this now.