patch 8.1.0023: gcc 8.1 warns for use of strncpy()

Problem:    gcc 8.1 warns for use of strncpy(). (John Marriott)
Solution:   Use mch_memmove() instead of STRNCPY().
diff --git a/src/version.c b/src/version.c
index 0cfe61a..69e20cb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    23,
+/**/
     22,
 /**/
     21,