patch 8.1.1856: popup preview test fails sometimes

Problem:    popup preview test fails sometimes. (Christian Brabandt)
Solution:   Clear the command line.
diff --git a/src/version.c b/src/version.c
index 28fd2a7..f7be012 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1856,
+/**/
     1855,
 /**/
     1854,