increase aerc check-mail timeout

due to purelymail backend (issue 213)

modules/common/mail/aerc.nix

@@ -176,6 +176,7 @@
         extraAccounts = {
           check-mail = "5m";
           check-mail-cmd = "${pkgs.isync}/bin/mbsync -a";
+          check-mail-timeout = "15s";
         };
       };