Fix pasto in class name

Author: stoned

doc/Type/IO/Spec/Cygwin.pod6

@@ -4,7 +4,7 @@
 
 =SUBTITLE Platform specific operations on file and directory paths for Cygwin
 
-    class IO::Spec::QNX is IO::Spec::Unix { }
+    class IO::Spec::Cygwin is IO::Spec::Unix { }
 
 An object of this type is available via the variable C<$*SPEC> if the
 Raku interpreter is running on C<Cygwin>.