[geary] Fix vala binding generation with webkit2gtk 2.17.4

[Rico Tzschichholz <ricotz src gnome org>]

commit 1d0aac1dfe461bf731b022381f179c0f48923834
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Mon Jun 26 16:49:02 2017 +0200

    Fix vala binding generation with webkit2gtk 2.17.4

 bindings/metadata/WebKit2-4.0.metadata |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/bindings/metadata/WebKit2-4.0.metadata b/bindings/metadata/WebKit2-4.0.metadata
index ad053ee..3e3044f 100644
--- a/bindings/metadata/WebKit2-4.0.metadata
+++ b/bindings/metadata/WebKit2-4.0.metadata
@@ -12,3 +12,4 @@ WebResource
   .failed#signal.error type="GLib.Error"
 WebView
   .load_failed#signal.error type="GLib.Error"
+  .show_option_menu#signal skip