Added require YAML
Added require YAML

This may be due to a dependency version. It has resolve issues running `Virtual Box 4.3.20` and `Vagrant 1.7.1`
merchantguru/trellis,mAAdhaTTah/bedrock-ansible,Twansparant/trellis-db-sync,jeffstieler/bedrock-ansible,all9lives/trellis,buluma/trellis,jvandijk/epwp-trellis,pressbooks/trellis,webdev1001/bedrock-ansible,proteusthemes/pt-ops,afonsoduarte/ansible-stacey,rpkoller/trellis,fullyint/trellis,partounian/trellis,buluma/trellis,newtonne/trellis,NicBeltramelli/trellis,mAAdhaTTah/bedrock-ansible,kalenjohnson/trellis,partounian/trellis,rogeruiz/trellis,mlaa/trellis,dmin7b5/trellis,cimocimocimo/cimo-wordpress-server,SecureCloud-biz/trellis,afonsoduarte/ansible-stacey,cimocimocimo/cimo-wordpress-server,BrandonShutter/trellis,jvandijk/trellis,ThemeSurgeon/trellis,Seravo/wp-palvelu-vagrant,jeffstieler/bedrock-ansible,dboune/trellis,roots/bedrock-ansible,jwall/trellis,ckovey/trellis,bbttxu/trellis,proteusthemes/pt-ops,skynet/trellis,Twansparant/trellis-db-sync,jeffstieler/bedrock-ansible,jvandijk/epwp-trellis,mlaa/trellis,alan-c/trellis,buluma/trellis,austinpray/bedrock-ansible,NicBeltramelli/trellis,jwkicklighter/trellis,roots/bedrock-ansible,buluma/trellis,louim/bedrock-ansible,ckovey/trellis,patrickheeney/trellis,drewrawitz/wp-ansible,NicBeltramelli/trellis,fullyint/trellis,evanfuture/trellis,Twansparant/trellis-db-sync,kulturavashchi/trellis,ChilliCreative/trellis,fullyint/trellis,mAAdhaTTah/bedrock-ansible,enricodeleo/bedrock-ansible,NicBeltramelli/trellis,cimocimocimo/cimo-wordpress-server,proteusthemes/pt-ops,kalenjohnson/trellis,roots/trellis,cimocimocimo/cimo-wordpress-server,fullyint/trellis,brettwise/bedrock-ansible,mAAdhaTTah/bedrock-ansible,dailysecret/trellis,kalenjohnson/trellis,dboune/trellis,BrandonShutter/trellis,Seravo/wp-vagrant,fusionpig/trellis,windeck/ansible-bedrock,ChilliCreative/trellis,Twansparant/trellis-db-sync,alan-c/trellis,all9lives/trellis,newtonne/trellis,newtonne/trellis,drawcard/trellis,roots/trellis,JacobDorman/bedrock-ansible,partounian/trellis,creditera/trellis,partounian/trellis,kalenjohnson/trellis,dailysecret/trellis,erikbelusic/trellis,pressbooks/trellis