[gbrainy] appdata: Mark missing string for translation

[Piotr Drąg <piotrdrag src gnome org>]

commit 2e99b86f68facd02bb81d45c9b573bd641add7fb
Author: Piotr Drąg <piotrdrag gmail com>
Date:   Sun Dec 17 17:27:17 2017 +0100

    appdata: Mark missing string for translation

 data/gbrainy.appdata.xml.in |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/data/gbrainy.appdata.xml.in b/data/gbrainy.appdata.xml.in
index a152ae8..1b3d1bc 100644
--- a/data/gbrainy.appdata.xml.in
+++ b/data/gbrainy.appdata.xml.in
@@ -4,7 +4,7 @@
   <id>org.gnome.gbrainy.desktop</id>
   <metadata_license>CC0</metadata_license>
   <project_license>GPL-2.0+</project_license>
-  <summary>gbrainy is a game to train memory, arithmetical and logical capabilities with many sorts of 
exercises of different difficulty levels</summary>
+  <_summary>gbrainy is a game to train memory, arithmetical and logical capabilities with many sorts of 
exercises of different difficulty levels</_summary>
   <description>
     <_p>
     gbrainy is a game to train memory, arithmetical and logical capabilities