v2.0.3
Serialize all communication with URLSessionWebSocketTask on the delegate queue.
This is an attempt to fix a problem in which URLSessionWebSocketTask occassionally throws this exception:
Fatal error: Only one of message or error should be nil: file /AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/swiftlang_overlay_Foundation/swiftlang-1103.8.25.8/swift/stdlib/public/Darwin/Foundation/URLSession.swift, line 46