[gardening] Corrected comment.

Author: nate-chandler

include/swift/AST/Decl.h

@@ -2862,7 +2862,7 @@ class GenericTypeDecl : public GenericContext, public TypeDecl {
 /// code. One is formed implicitly when a declaration is written with an opaque
 /// result type, as in:
 ///
-/// func foo() -> opaque SignedInteger { return 1 }
+/// func foo() -> some SignedInteger { return 1 }
 ///
 /// The declared type is a special kind of ArchetypeType representing the
 /// abstracted underlying type.