Use <iostream> instead of <iostream.h> in Example Code for PCH

This old header seems to have been forgotten in one of the example files
(UNSTABLE.H).

Signed-off-by: Ted Lyngmo <[email protected]>

Author: TedLyngmo

docs/build/creating-precompiled-header-files.md

@@ -247,7 +247,7 @@ void savetime( void );
 //
 #ifndef __UNSTABLE_H
 #define __UNSTABLE_H
-#include<iostream.h>
+#include<iostream>
 void notstable( void );
 #endif // __UNSTABLE_H
 ```