patch 8.1.0393: not all white space difference options available

Problem:    Not all white space difference options available.
Solution:   Add "iblank", "iwhiteall" and "iwhiteeol" to 'diffopt'.
diff --git a/src/version.c b/src/version.c
index d04bdab..13b8aed 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    393,
+/**/
     392,
 /**/
     391,