patch 8.1.1556: command for failing screenshot does not include directory

Problem:    The command displayed to show a failing screenshot does not include
            the "testdir" directory.
Solution:   Prefix the directory name so that it can be copy-pasted.

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1556,
 /**/
     1555,
 /**/