patch 8.1.1838: there is :spellwrong and :spellgood but not :spellrare

Problem:    There is :spellwrong and :spellgood but not :spellrare.
Solution:   Add :spellrare. (Martin Tournoij, closes #4291)
diff --git a/src/version.c b/src/version.c
index 77d9406..fbc1db9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1838,
+/**/
     1837,
 /**/
     1836,