Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/channel.txt b/runtime/doc/channel.txt
index f0d459b..9cc2be3 100644
--- a/runtime/doc/channel.txt
+++ b/runtime/doc/channel.txt
@@ -1,4 +1,4 @@
-*channel.txt*      For Vim version 8.0.  Last change: 2018 Apr 18
+*channel.txt*      For Vim version 8.1.  Last change: 2018 Apr 18
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar