Omit mkPolyline from tvOS 8, watchOS builds

[1ec5]

Fixed the following compilation errors on tvOS and watchOS introduced by #39:

/path/to/Polyline/Polyline/Polyline.swift
/path/to/Polyline/Polyline/Polyline.swift:59:28: 'MKPolyline' is only available on tvOS 9.2 or newer
/path/to/Polyline/Polyline/Polyline.swift:59:28: Add @available attribute to enclosing var
/path/to/Polyline/Polyline/Polyline.swift:59:28: Add @available attribute to enclosing struct
/path/to/Polyline/Polyline/Polyline.swift:61:26: 'MKPolyline' is only available on tvOS 9.2 or newer
/path/to/Polyline/Polyline/Polyline.swift:61:26: Add 'if #available' version check
/path/to/Polyline/Polyline/Polyline.swift:61:26: Add @available attribute to enclosing var
/path/to/Polyline/Polyline/Polyline.swift:61:26: Add @available attribute to enclosing struct

/path/to/Polyline/Polyline/Polyline.swift
/path/to/Polyline/Polyline/Polyline.swift:59:28: Use of undeclared type 'MKPolyline'
/path/to/Polyline/Polyline/Polyline.swift:61:26: Use of unresolved identifier 'MKPolyline'
/path/to/Polyline/Polyline/Polyline.swift:59:16: Did you mean 'mkPolyline'?
/path/to/Polyline/Polyline/Polyline.swift:41:15: Did you mean 'Polyline'?

/cc @tomtaylor @frederoni

[1ec5]

@tomtaylor @raphaelmor, can you take a look? (For what it’s worth, I’d be happy to help out as a collaborator, since I maintain some libraries that depend on this library.)

[raphaelmor]

I'm adding you as a collaborator, if @tomtaylor is fine with, the more the merrier (and I can't contribute anymore :( )

[tomtaylor]

Absolutely!

…

On 9 Mar 2017, at 14:39, Raphaël Mor ***@***.***> wrote: I'm adding you as a collaborator, if @tomtaylor is fine with, the more the merrier (and I can't contribute anymore :( ) — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or mute the thread.

[1ec5]

Thanks!