Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/windows.txt b/runtime/doc/windows.txt
index c6c8cad..e88cfcb 100644
--- a/runtime/doc/windows.txt
+++ b/runtime/doc/windows.txt
@@ -1,4 +1,4 @@
-*windows.txt*   For Vim version 8.0.  Last change: 2018 Apr 24
+*windows.txt*   For Vim version 8.1.  Last change: 2018 Apr 24
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar