generate media/revision.txt for dev server

This should create https://developer-dev.allizom.org/media/revision.txt so we can add Dev to [our whatsdeployed page](https://whatsdeployed.paas.allizom.org/?owner=mozilla&repo=kuma&name[]=Stage&url[]=https://developer.allizom.org/media/revision.txt&name[]=Prod&url[]=https://developer.mozilla.org/media/revision.txt)