chore: bump app vsns

apps/emqx/src/emqx.app.src

@@ -2,7 +2,7 @@
 {application, emqx, [
     {id, "emqx"},
     {description, "EMQX Core"},
-    {vsn, "5.1.19"},
+    {vsn, "5.1.20"},
     {modules, []},
     {registered, []},
     {applications, [