Make all meta.maintainers attributes lists

(cherry picked from commit b714f552392310cd23b8e71402dfa64b629d2190)
The two new changes were really missing on master.

pkgs/applications/misc/synapse/default.nix

···
       '';
       homepage = https://launchpad.net/synapse-project;
       license = stdenv.lib.licenses.gpl3;
-      maintainers = with stdenv.lib.maintainers; mahe;
+      maintainers = with stdenv.lib.maintainers; [ mahe ];
       platforms = with stdenv.lib.platforms; all;
   };
 }

pkgs/tools/system/iops/default.nix

···
     '';
     homepage = http://www.vanheusden.com/iops/;
     license = licenses.gpl2;
-    maintainers = with maintainers; davidak;
+    maintainers = with maintainers; [ davidak ];
     platforms = platforms.linux; # build problems on Darwin
   };
 }