release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/workshop.txt b/runtime/doc/workshop.txt
index d9268f3..f71866d 100644
--- a/runtime/doc/workshop.txt
+++ b/runtime/doc/workshop.txt
@@ -1,4 +1,4 @@
-*workshop.txt*  For Vim version 8.2.  Last change: 2019 Jan 17
+*workshop.txt*  For Vim version 9.0.  Last change: 2019 Jan 17
 
 
 		  VIM REFERENCE MANUAL    by Gordon Prieur