swift-package-manager

Corrected tvOS platform identifiers.

I noticed that when building a project whose `.xcodeproj` was generated via SPM via Carthage, the build would fail with:

    Parse error: unexpected SDK key "tvos"

So I created a tvOS project right from Xcode itself and ran

    xcodebuild -project Foo.xcodeproj -target Foo -showBuildSettings | grep PLATFORMS

which returned this:

    SUPPORTED_PLATFORMS = appletvos appletvsimulator

So I replaced

    tvos tvsimulator

as found in `MyProject.xcodeproj/Configs/Project.xcconfig` with 

    appletvos appletvsimulator

and carthage now builds successfully.