patch 8.1.1183: typos in VisVim comments

Problem:    Typos in VisVim comments.
Solution:   Correct the typos. (Christ van Willegen)
diff --git a/src/VisVim/README_VisVim.txt b/src/VisVim/README_VisVim.txt
index 25b0fbd..d96becf 100644
--- a/src/VisVim/README_VisVim.txt
+++ b/src/VisVim/README_VisVim.txt
@@ -238,7 +238,7 @@
 - Added an option to do a :cd before opening the file (having a file opened
   by clicking it but finding out to be still in C:\Windows\system when trying to
   open another file by ":e" can be annoying). Change directory can be
-  done to the source file's directory or it's parent directory.
+  done to the source file's directory or its parent directory.
 - Added some explanations to the error message for the CO_E_CLASSSTRING error
   ("Use OLE Vim and make sure to register...").