Define provider as virtualbox to avoid failure
Define provider as virtualbox to avoid failure

If the user has a different default provider, e.g., parallels, `vagrant up` fails. Might as well as define this since this is currently only compatible with Virtualbox, as far as I know.

mAAdhaTTah/bedrock-ansible,proteusthemes/pt-ops,fullyint/trellis,newtonne/trellis,bbttxu/trellis,buluma/trellis,erikbelusic/trellis,roots/trellis,merchantguru/trellis,drawcard/trellis,NicBeltramelli/trellis,skynet/trellis,rpkoller/trellis,NicBeltramelli/trellis,partounian/trellis,SecureCloud-biz/trellis,kalenjohnson/trellis,all9lives/trellis,partounian/trellis,cimocimocimo/cimo-wordpress-server,jvandijk/epwp-trellis,dmin7b5/trellis,dailysecret/trellis,pressbooks/trellis,roots/trellis,NicBeltramelli/trellis,Twansparant/trellis-db-sync,jeffstieler/bedrock-ansible,creditera/trellis,fullyint/trellis,alan-c/trellis,cimocimocimo/cimo-wordpress-server,kalenjohnson/trellis,dboune/trellis,ckovey/trellis,ckovey/trellis,buluma/trellis,louim/bedrock-ansible,partounian/trellis,newtonne/trellis,mlaa/trellis,ChilliCreative/trellis,fusionpig/trellis,jvandijk/trellis,dailysecret/trellis,BrandonShutter/trellis,jeffstieler/bedrock-ansible,alan-c/trellis,dboune/trellis,cimocimocimo/cimo-wordpress-server,ThemeSurgeon/trellis,ChilliCreative/trellis,rogeruiz/trellis,fullyint/trellis,mlaa/trellis,proteusthemes/pt-ops,mAAdhaTTah/bedrock-ansible,jvandijk/epwp-trellis,roots/bedrock-ansible,austinpray/bedrock-ansible,Twansparant/trellis-db-sync,fullyint/trellis,cimocimocimo/cimo-wordpress-server,proteusthemes/pt-ops,BrandonShutter/trellis,afonsoduarte/ansible-stacey,buluma/trellis,Twansparant/trellis-db-sync,buluma/trellis,kulturavashchi/trellis,patrickheeney/trellis,newtonne/trellis,pressbooks/trellis,NicBeltramelli/trellis,roots/bedrock-ansible,jeffstieler/bedrock-ansible,kalenjohnson/trellis,afonsoduarte/ansible-stacey,Twansparant/trellis-db-sync,partounian/trellis,mAAdhaTTah/bedrock-ansible,jwall/trellis,mAAdhaTTah/bedrock-ansible,jwkicklighter/trellis,drewrawitz/wp-ansible,all9lives/trellis,kalenjohnson/trellis,evanfuture/trellis