patch 9.0.0587: Unicode tables are outdated

Problem:    Unicode tables are outdated.
Solution:   Update to Unicode release 15. (Christian Brabandt, closes #11220)
diff --git a/src/version.c b/src/version.c
index 30fe48d..8c9cc5c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    587,
+/**/
     586,
 /**/
     585,