fixes typo in Vagrantfile for mon-prod hostname
fixes typo in Vagrantfile for mon-prod hostname

Unlike all other VMs, the mon-prod box wasn't getting a hostname
assigned, due to a typo in the declaration. The line
that should have been setting the hostname was reusing the "box"
declaration. Spectests caught this.

mark-in/securedrop-prov-upstream,mark-in/securedrop-prov-upstream,mark-in/securedrop-prov-upstream,mark-in/securedrop-prov-upstream