Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/mbyte.txt b/runtime/doc/mbyte.txt
index c25eb64..99ce10f 100644
--- a/runtime/doc/mbyte.txt
+++ b/runtime/doc/mbyte.txt
@@ -1,4 +1,4 @@
-*mbyte.txt*     For Vim version 8.0.  Last change: 2018 Jan 21
+*mbyte.txt*     For Vim version 8.1.  Last change: 2018 Jan 21
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar et al.