Update summary in metainfo

lib/xdg/org.telegram.desktop.metainfo.xml

@@ -4,7 +4,7 @@
     <metadata_license>CC0-1.0</metadata_license>
     <project_license>GPL-3.0</project_license>
     <name>Telegram Desktop</name>
-    <summary>Fast. Secure. Powerful.</summary>
+    <summary>Fast and secure messaging app</summary>
     <description>
         <p>Pure instant messaging — simple, fast, secure, and synced across all your devices. One of the world's top 10 most downloaded apps with over 500 million active users.</p>
         <p>FAST: Telegram is the fastest messaging app on the market, connecting people via a unique, distributed network of data centers around the globe.</p>