Add refresh rate option

Bitrate for 4k@60 seems to be slightly too high, which causes artifacts and cut-outs. Lock to 30fps.

sway/displays.pl

@@ -92,6 +92,7 @@ my %configs = (
             'width' => 3840,
             'height' => 2160,
             'x' => 900,
+            'refresh' => 30,
             'y' => 0,
             'rotate' => 0,
             'scale' => 1.33333,
@@ -128,6 +129,7 @@ my %configs = (
             'on' => 1,
             'width' => 3840,
             'height' => 2160,
+            'refresh' => 30,
             'x' => 0,
             'y' => 0,
             'rotate' => 0,
@@ -411,7 +413,7 @@ foreach my $out (keys %$on) {
             defined $on->{$out}->{height} )
         {
             $cmd .= " mode $on->{$out}->{width}x" .
-                "$on->{$out}->{height}";
+                "$on->{$out}->{height}" .
         }
         if (defined $on->{$out}->{bg} &&
             -f $on->{$out}->{bg})