update @nativescript/ios to the recent version

[madmas]

Hi @farfromrefug
is there a reason that @nativescript/iosdependency in this repo is still at 6.5.6 ?
Updating it to a recent version would help me with nativescript-community/ui-mapbox#93

WDYT ?

[farfromrefug]

@madmas it was not stable enough. We can upgrade it now. Though it should not crash. Would like to fix your issue with 6.5.6