docs: Update Windows installation instructions in setup-vagrant.md.
docs: Update Windows installation instructions in setup-vagrant.md.

Vagrant 1.8.6 is only compatible with VirtualBox <= 5.1, so I made a
note to use version < 5.2.

hackerkid/zulip,tommyip/zulip,rishig/zulip,zulip/zulip,showell/zulip,brainwane/zulip,timabbott/zulip,zulip/zulip,kou/zulip,rishig/zulip,jackrzhang/zulip,tommyip/zulip,rht/zulip,jackrzhang/zulip,punchagan/zulip,shubhamdhama/zulip,showell/zulip,rishig/zulip,dhcrzf/zulip,showell/zulip,punchagan/zulip,timabbott/zulip,synicalsyntax/zulip,dhcrzf/zulip,hackerkid/zulip,dhcrzf/zulip,hackerkid/zulip,punchagan/zulip,shubhamdhama/zulip,hackerkid/zulip,tommyip/zulip,tommyip/zulip,hackerkid/zulip,andersk/zulip,andersk/zulip,jackrzhang/zulip,eeshangarg/zulip,rishig/zulip,tommyip/zulip,shubhamdhama/zulip,jackrzhang/zulip,synicalsyntax/zulip,punchagan/zulip,kou/zulip,hackerkid/zulip,zulip/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,zulip/zulip,brainwane/zulip,synicalsyntax/zulip,showell/zulip,eeshangarg/zulip,jackrzhang/zulip,rht/zulip,synicalsyntax/zulip,kou/zulip,punchagan/zulip,rht/zulip,timabbott/zulip,brainwane/zulip,brainwane/zulip,dhcrzf/zulip,eeshangarg/zulip,rishig/zulip,timabbott/zulip,synicalsyntax/zulip,rht/zulip,showell/zulip,eeshangarg/zulip,timabbott/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,dhcrzf/zulip,jackrzhang/zulip,rishig/zulip,eeshangarg/zulip,rht/zulip,shubhamdhama/zulip,kou/zulip,showell/zulip,jackrzhang/zulip,rht/zulip,shubhamdhama/zulip,shubhamdhama/zulip,brainwane/zulip,zulip/zulip,rishig/zulip,tommyip/zulip,dhcrzf/zulip,rht/zulip,andersk/zulip,synicalsyntax/zulip,kou/zulip,andersk/zulip,punchagan/zulip,brainwane/zulip,showell/zulip,timabbott/zulip,synicalsyntax/zulip,andersk/zulip,brainwane/zulip,andersk/zulip,zulip/zulip,timabbott/zulip,zulip/zulip,tommyip/zulip,kou/zulip,shubhamdhama/zulip,dhcrzf/zulip