release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/if_sniff.txt b/runtime/doc/if_sniff.txt
index de6d8eb..27db688 100644
--- a/runtime/doc/if_sniff.txt
+++ b/runtime/doc/if_sniff.txt
@@ -1,4 +1,4 @@
-*if_sniff.txt*	For Vim version 8.2.  Last change: 2016 Feb 27
+*if_sniff.txt*	For Vim version 9.0.  Last change: 2016 Feb 27
 
 
 		  VIM REFERENCE MANUAL