Update to Swift 5.3

[Danappelxx]

Hi! Not sure if this package is maintained anymore, but I spent a little time upgrading it to the latest Swift version and it seems to work just fine.

Somewhere along the line, the code should be refactored to take advantage of new features such as Codable, but in the meantime this is enough to get it running again.

I didn't find unit tests, but in my own app I am:

• successfully authenticating
• listing devices
• fetching detailed device information
• calling functions on devices
• reading variables from devices
  ...which gives me hope that the rest of the features work as well.

[Danappelxx]

Bump!