Remove explicit type annotation that can be inferred

Author: iv-mexx

Sources/SignalProducer.swift

@@ -1891,7 +1891,7 @@ extension SignalProducerProtocol {
 	///            each value from the original producer to the inner producer corresponding 
 	///            to the group to which the value belongs to (as determined by the key)
 	public func group<Key: Hashable>(by grouping: @escaping (Value) -> Key) -> SignalProducer<(Key, SignalProducer<Value, Error>), Error> {
-		return SignalProducer<(Key, SignalProducer<Value, Error>), Error> { observer, disposable in
+		return SignalProducer { observer, disposable in
 			let groups = Atomic<[Key: Signal<Value, Error>.Observer]>([:])
 
 			disposable += self.start { event in