Use forEach instead of for...of (fixes #3449)

[walaszczykm]

Description:
As described on #3449 if you want to build project which depends on aframe it fails because of ES6 syntax on aframe-master.js:75038. This code comes from a-register-element.js:62

Changes proposed:
I have changed for..of loop:

for (var propName of Object.getOwnPropertyNames(newObj.prototype)){}

to forEach function call:

Object.getOwnPropertyNames(newObj.prototype).forEach(function(propName){})

[walaszczykm]

npm run test:firefox -- --single-run crashes for me also on master branch without any changes

[machenmusik]

Yeah, I ran into that while doing #3489 as well. Maybe you can try forcing an empty commit to get it to try again?

[dmarcos]

I restarted the tests

[machenmusik]

yay tests passed

[dmarcos]

Thanks!