Update STL MIME type

Since march, there is now an official MIME type for STL files. See https://www.iana.org/assignments/media-types/model/stl for the new MIME type specification.

Fixes #4141.

cura.desktop.in

@@ -13,6 +13,6 @@ TryExec=@CMAKE_INSTALL_FULL_BINDIR@/cura
 Icon=cura-icon
 Terminal=false
 Type=Application
-MimeType=application/sla;application/vnd.ms-3mfdocument;application/prs.wavefront-obj;image/bmp;image/gif;image/jpeg;image/png;model/x3d+xml;
+MimeType=model/stl;application/vnd.ms-3mfdocument;application/prs.wavefront-obj;image/bmp;image/gif;image/jpeg;image/png;model/x3d+xml;
 Categories=Graphics;
 Keywords=3D;Printing;Slicer;

cura.sharedmimeinfo

@@ -6,7 +6,7 @@
         <glob-deleteall/>
         <glob pattern="*.3mf"/>
     </mime-type>
-    <mime-type type="application/sla">
+    <mime-type type="model/stl">
         <comment>Computer-aided design and manufacturing format</comment>
         <icon name="unknown"/>
         <glob-deleteall/>