patch 8.0.0659: no test for conceal mode

Problem:    No test for conceal mode.
Solution:   Add a conceal mode test. (Dominique Pelle, closes #1783)
diff --git a/src/version.c b/src/version.c
index ab0381c..cb4ac7f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    659,
+/**/
     658,
 /**/
     657,