use older expr syntax for backwards compatibility with the expr that comes with OSX

plugins/better-alias/balias.fish

 function balias --argument alias command
   eval 'alias $alias $command'
-  if expr match $command '^sudo '>/dev/null
+  if expr $command : '^sudo '>/dev/null
     set command (expr substr + $command 6 (expr length $command))
   end
   complete -c $alias -xa "(