Try to make format_muted width more consistent

Most of numbers from 0 to 100 have 2 digits.

dotfiles/i3status.conf

@@ -39,7 +39,7 @@ disk "/home" {
 
 volume master {
     format          = "♪%volume"
-    format_muted    = "♪---%%"
+    format_muted    = "♪--%%"
     device          = "default"
     mixer           = "Master"
     mixer_idx       = 0