patch 8.1.0237: Ruby on Cygwin doesn't always work

Problem:    Ruby on Cygwin doesn't always work.
Solution:   Use LIBRUBY_SO if LIBRUBY_ALIASES isn't set. (Ken Takata)
diff --git a/src/version.c b/src/version.c
index ec097fd..de3a32e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    237,
+/**/
     236,
 /**/
     235,