patch 8.2.3109: check for $DISPLAY never fails

Problem:    Check for $DISPLAY never fails.
Solution:   Use eval().
diff --git a/src/version.c b/src/version.c
index 9b1ac9a..a36ec80 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3109,
+/**/
     3108,
 /**/
     3107,