Make PromiseInitClosure @escaping

Seeing this error when using `PromiseInitClosure`:

> Closure use of non-escaping parameter 'fulfill' may allow it to escape

Author: KevM

SwiftTask/SwiftTask.swift

@@ -67,7 +67,7 @@ open class Task<Progress, Value, Error>: Cancellable, CustomStringConvertible
     public typealias RejectHandler = (Error) -> Void
     public typealias Configuration = TaskConfiguration
 
-    public typealias PromiseInitClosure = (_ fulfill: FulfillHandler, _ reject: RejectHandler) -> Void
+    public typealias PromiseInitClosure = (_ fulfill: @escaping FulfillHandler, _ reject: @escaping RejectHandler) -> Void
     public typealias InitClosure = (_ progress: @escaping ProgressHandler, _ fulfill: @escaping FulfillHandler, _ reject: @escaping RejectHandler, _ configure: TaskConfiguration) -> Void
 
     internal typealias _Machine = _StateMachine<Progress, Value, Error>