Correct typo

Co-authored-by: AsciiWolf <[email protected]>

Author: cengique

Diff for: misc/io.github.grangerhub.Tremulous.appdata.xml

@@ -10,7 +10,7 @@
   <launchable type="desktop-id">io.github.grangerhub.Tremulous.desktop</launchable>
   <name>Tremulous</name>
   <developer_name>Dark Legion Development and GrangerHub</developer_name>
-  <summary>Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy (Grangerhub version)</summary>
+  <summary>Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy (GrangerHub version)</summary>
   <description>
     <p>
       Tremulous is a free, open source game that blends a team based FPS with