Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index 1157e15..f569ec5 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1,4 +1,4 @@
-*index.txt*     For Vim version 8.0.  Last change: 2018 Apr 19
+*index.txt*     For Vim version 8.1.  Last change: 2018 Apr 19
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar