patch 8.1.0104: can't build without the +eval feature

Problem:    Can't build without the +eval feature.
Solution:   Add #ifdef.
diff --git a/src/version.c b/src/version.c
index 45f339b..e2ccc11 100644
--- a/src/version.c
+++ b/src/version.c
@@ -779,6 +779,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    104,
+/**/
     103,
 /**/
     102,