patch 8.2.0541: Travis CI does not give compiler warnings

Problem:    Travis CI does not give compiler warnings.
Solution:   Add flags for warnings.  Fix uncovered problems. (Ozaki Kiichi,
            closes #5898)
diff --git a/src/version.c b/src/version.c
index be24594..b170d4a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    541,
+/**/
     540,
 /**/
     539,