patch 9.0.1418: the included xdiff code is a bit outdated

Problem:    The included xdiff code is a bit outdated.
Solution:   Sync with the latest git xdiff code. (Yee Cheng Chin,
            closes #12181)
diff --git a/src/version.c b/src/version.c
index e20eb06..45be73e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1418,
+/**/
     1417,
 /**/
     1416,