doc(linux, metainfo): cannot have two screenshots defaults

Author: Irineu333

application/installation/com.neoutils.NeoRegex.metainfo.xml

@@ -37,7 +37,7 @@
             <caption>NeoRegex in Dark Mode</caption>
         </screenshot>
 
-        <screenshot type="default">
+        <screenshot>
             <image>
                 https://raw.githubusercontent.com/NeoUtils/NeoRegex/1bd2a74185c302e8776edfadb41615955c393be5/images/linux-light-mode.png
             </image>