r235 safari bug in service worker loader

=>[/code:1y0q0nrl] which is supported only ES6. This isn't supported by Safari and Safari stops loading with the following error

[code:1y0q0nrl]SyntaxError: Unexpected token '>'

at

.then(reg => console.log("Registered service worker on " + reg.scope))
[/code:1y0q0nrl]

[b]Steps to Reproduce Bug[/b]
[ul]
    [li] Export and HTML game
    [/li][li] Load it in Safari (I'm using 9.1.3 on MacOS 10.11)[/li][/ul]
    
[b]Observed Result[/b]
The game doesn't load due to a JS syntax error
    
[b]Expected Result[/b]
The game should load.
    
[b]Affected Browsers[/b]
[ul]
    [li] Safari[/li][/ul]
    
[b]Operating System and Service Pack[/b]
MacOS 10.11
    
[b]Construct 2 Version ID[/b]
r235 beta