add explicit deps on net-ssh(-multi) and highline
add explicit deps on net-ssh(-multi) and highline

tas50/knife-ec2,juliandunn/knife-ec2,MsysTechnologiesllc/knife-ec2,zillabyte/knife-ec2,ivantsepp/knife-ec2,pallan/knife-ec2,tily/ruby-knife-nc,chef/knife-ec2,TheNeatCompany/knife-ec2,smith/knife-ec2,MsysTechnologiesllc/knife-ec2,evertrue/knife-ec2,paperlesspost/knife-ec2,chef/knife-ec2,cloudant/knife-ec2,ClogenyTechnologies/knife-ec2,thommay/knife-ec2,DataDog/knife-ec2,4current/knife-ec2,jlindsey/knife-ec2