Update SpaceCadetPinball.metainfo.xml

Shortened summary and removed period.
#178

Platform/Linux/SpaceCadetPinball.metainfo.xml

@@ -3,7 +3,7 @@
     <id>com.github.k4zmu2a.spacecadetpinball</id>
     <name>Space Cadet Pinball</name>
     <display_name>Space Cadet Pinball</display_name>
-    <summary>Reverse engineering of 3D Pinball for Windows - Space Cadet, a game bundled with Windows.</summary>
+    <summary>Game engine for Space Cadet Pinball</summary>
     <url type="homepage">https://github.com/k4zmu2a/SpaceCadetPinball</url>
     <url type="bugtracker">https://github.com/k4zmu2a/SpaceCadetPinball/issues</url>
     <description>