Fixed bug with lang::choice

The documentation currently says %count% is automatically replaced with the count when using `Lang::choice`, but this is wrong.

The current function adds a keyless item to the $replace array containing $number - if you don't provide an array of other strings to replace, it will be `[0] => $number`.

The way Laravel does replacement in translation, this obviously does nothing. With this change, `:count` will be replaced with $number. I'm not sure if this is desired behavior or not, but the current implementation surely can't be intentional.