Apply Joe H's suggestions from code review

Co-authored-by: Joseph Heck <[email protected]>

Author: invalidname

stdlib/public/Concurrency/AsyncStream.swift

@@ -229,7 +229,7 @@ public struct AsyncStream<Element> {
   ///   instance that it uses to provide elements to the stream and terminate the
   ///   stream when finished.
   ///
-  /// The `AsyncStream.Contuation` received by the `build` closure is appopriate
+  /// The `AsyncStream.Continuation` received by the `build` closure is appopriate
   /// for use in concurrent contexts. It is thread safe to send and finish; all
   /// calls are to the continuation are serialized, however calling this from
   /// multiple concurrent contexts could result in out-of-order delivery.

stdlib/public/Concurrency/AsyncThrowingStream.swift

@@ -258,7 +258,7 @@ public struct AsyncThrowingStream<Element, Failure: Error> {
   ///   `AsyncThrowingStream.Continuation` instance that it uses to provide
   ///   elements to the stream and terminate the stream when finished.
   ///
-  /// The `AsyncThrowingStream.Contuation` received by the `build` closure is
+  /// The `AsyncThrowingStream.Continuation` received by the `build` closure is
   /// appopriate for use in concurrent contexts. It is thread safe to send and
   /// finish; all calls are to the continuation are serialized, however calling
   /// this from multiple concurrent contexts could result in out of order