AST: Fix overly suspenseful comment

Author: slavapestov

include/swift/AST/Type.h

@@ -282,13 +282,11 @@ class Type {
   /// Transform the given type by recursively applying the user-provided
   /// function to each node.
   ///
-  /// If the function returns \c None, the transform operation will
-  ///
   /// \param fn A function object which accepts a type pointer and returns a
   /// transformed type, a null type (which will propagate out the null type),
   /// or None (to indicate that the transform operation should recursively
   /// transform the children). The function object should use \c dyn_cast rather
-  /// than \c getAs when the transform is intended to preserve sugar
+  /// than \c getAs when the transform is intended to preserve sugar.
   ///
   /// \returns the result of transforming the type.
   Type transformRec(llvm::function_ref<Optional<Type>(TypeBase *)> fn) const;