Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/gui_x11.txt b/runtime/doc/gui_x11.txt
index b1c2cc6..8a5e9bf 100644
--- a/runtime/doc/gui_x11.txt
+++ b/runtime/doc/gui_x11.txt
@@ -1,4 +1,4 @@
-*gui_x11.txt*   For Vim version 8.0.  Last change: 2018 May 06
+*gui_x11.txt*   For Vim version 8.1.  Last change: 2018 May 06
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar