[vte] app: Fix option output in help

[Christian Persch <chpe src gnome org>]

commit 6d7e27736203c9210a3e4fec2cc44efcf9890d84
Author: Christian Persch <chpe src gnome org>
Date:   Tue Mar 27 19:40:13 2018 +0200

    app: Fix option output in help

 src/app/app.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/app/app.cc b/src/app/app.cc
index d424064..82f38ff 100644
--- a/src/app/app.cc
+++ b/src/app/app.cc
@@ -354,7 +354,7 @@ public:
                         { "debug", 'd', 0,G_OPTION_ARG_NONE, &debug,
                           "Enable various debugging checks", nullptr },
                         { "encoding", 0, 0, G_OPTION_ARG_STRING, &encoding,
-                          "Specify the terminal encoding to use", nullptr },
+                          "Specify the terminal encoding to use", "ENCODING" },
                         { "env", 0, 0, G_OPTION_ARG_FILENAME_ARRAY, &environment,
                           "Add environment variable to the child\'s environment", "VAR=VALUE" },
                         { "extra-margin", 0, 0, G_OPTION_ARG_INT, &extra_margin,