Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/usr_11.txt b/runtime/doc/usr_11.txt
index 31a53c0..13c08f9 100644
--- a/runtime/doc/usr_11.txt
+++ b/runtime/doc/usr_11.txt
@@ -1,4 +1,4 @@
-*usr_11.txt*	For Vim version 8.0.  Last change: 2018 Apr 13
+*usr_11.txt*	For Vim version 8.1.  Last change: 2018 Apr 13
 
 		     VIM USER MANUAL - by Bram Moolenaar