patch 8.0.0501: on MS-Windows ":!start" does not work as expected

Problem:    On MS-Windows ":!start" does not work as expected.
Solution:   When creating a process fails try passing the argument to
            ShellExecute().  (Katsuya Hino, closes #1570)
diff --git a/src/version.c b/src/version.c
index c3a4779..a1edd07 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    501,
+/**/
     500,
 /**/
     499,