Add whitelist add command

app/controllers/vouchers_controller.rb

@@ -25,7 +25,7 @@ class VouchersController < ApplicationController
       @voucher = Voucher.new(voucher_params)
       
       if @voucher.save
-        output = %x(mcrcon -c -H mine.vereto.net -p #{ENV["MC_RCON_PASS"]} "whitelist add #{params[:vouchee]}")
+        output = `mc-whitelist-users #{params[:vouchee]}`
         render json: { :message => output }.to_json, status: :created, location: @voucher
       else
        render json: @voucher.errors, status: :unprocessable_entity