release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/quotes.txt b/runtime/doc/quotes.txt
index 554e8af..181682d 100644
--- a/runtime/doc/quotes.txt
+++ b/runtime/doc/quotes.txt
@@ -1,4 +1,4 @@
-*quotes.txt*    For Vim version 8.2.  Last change: 2018 Mar 29
+*quotes.txt*    For Vim version 9.0.  Last change: 2018 Mar 29
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar