change metainfo release type to "stable"

To satisfy some arcane standard that's badly specified somewhere.

Signed-off-by: Stephen M. Cameron <stephenmcameron@gmail.com>

Author: smcameron

share/metainfo/io.github.smcameron.space-nerds-in-space.metainfo.xml.template

@@ -17,7 +17,7 @@
   <metadata_license>CC0-1.0</metadata_license>
   <project_license>GPL-2.0-or-later</project_license>
   <releases>
-  <release version=SNIS_VERSION date=TODAYS_DATE type="desktop-application"/>
+  <release version=SNIS_VERSION date=TODAYS_DATE type="stable"/>
   </releases>
   <description>
     <p>