patch 7.4.921
Problem:    Missing proto file update. (Randall W. Morris)
Solution:   Add the missing line for mch_ishidden.
diff --git a/src/version.c b/src/version.c
index eb418a7..3792aa0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    921,
+/**/
     920,
 /**/
     919,