xpdf: add license, update homepage

pkgs/applications/misc/xpdf/default.nix

···
       --set QT_PLUGIN_PATH ${qtbase.bin}/${qtbase.qtPluginPrefix}:${qtsvg.bin}/${qtbase.qtPluginPrefix}
   '';
 
-  meta = {
-    homepage = http://www.foolabs.com/xpdf/;
+  meta = with stdenv.lib; {
+    homepage = https://www.xpdfreader.com;
     description = "Viewer for Portable Document Format (PDF) files";
-
-    platforms = stdenv.lib.platforms.unix;
-    maintainers = [ stdenv.lib.maintainers.peti ];
+    license = with licenses; [ gpl2 gpl3 ];
+    platforms = platforms.unix;
+    maintainers = [ maintainers.peti ];
   };
 }