release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/if_lua.txt b/runtime/doc/if_lua.txt
index 00b51a8..63ee91a 100644
--- a/runtime/doc/if_lua.txt
+++ b/runtime/doc/if_lua.txt
@@ -1,4 +1,4 @@
-*if_lua.txt*    For Vim version 8.2.  Last change: 2021 Aug 06
+*if_lua.txt*    For Vim version 9.0.  Last change: 2021 Aug 06
 
 
 		  VIM REFERENCE MANUAL    by Luis Carvalho