Update heroku.md
Update heroku.md

Use `create` instead of deprecated `add` addons command
lisb/hubot,pchaigno/hubot,scboucher/hubot,rlugojr/hubot,lisb/hubot,ddmng/brazil82-hubot,github/hubot,skcript/skubot,PropertyUX/nubot,hubotio/hubot,decaffeinate-examples/hubot,hubotio/hubot,nandub/hubot,makii42/hubot,Mattlk13/Hubot,mrb/hubot,WaleedAshraf/hubot,scboucher/hubot,nandub/hubot,ouadie-lahdioui/hubot,github/hubot,PropertyUX/nubot,lisb/hubot,ClaudeBot/hubot,zvelo/hubot,decaffeinate-examples/hubot