vagrant: Add installation support for MacOS 10.15.6.
vagrant: Add installation support for MacOS 10.15.6.

There are file sharing issues with the mac version 10.15.6 and
vagrant. Using parallels as a provider for vagrant fixes the issue.

eeshangarg/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,rht/zulip,hackerkid/zulip,hackerkid/zulip,brainwane/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,brainwane/zulip,rht/zulip,punchagan/zulip,kou/zulip,andersk/zulip,showell/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,showell/zulip,hackerkid/zulip,zulip/zulip,brainwane/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,hackerkid/zulip,brainwane/zulip,brainwane/zulip,punchagan/zulip,andersk/zulip,kou/zulip,showell/zulip,punchagan/zulip,rht/zulip,rht/zulip,rht/zulip,showell/zulip,zulip/zulip,kou/zulip,punchagan/zulip,andersk/zulip,showell/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,showell/zulip,showell/zulip,punchagan/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,hackerkid/zulip,zulip/zulip,brainwane/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,punchagan/zulip,brainwane/zulip