Added appcasts to the hashicorps casks

Added appcasts from the releases.atom files of the Github repos of consul-web-ui, nomad, otto, packer, serf, vagrant, and vault

Casks/consul-web-ui.rb

@@ -4,6 +4,8 @@ cask 'consul-web-ui' do
 
   # hashicorp.com was verified as official when first introduced to the cask
   url "https://releases.hashicorp.com/consul/#{version}/consul_#{version}_web_ui.zip"
+  appcast 'https://github.com/hashicorp/consul/releases.atom',
+          checkpoint: '1583f51f8e4b3524aa5a0acb676e4d4bdbd25eb62637715a2e9a168ab7ce55a5'
   name 'Consul Web UI'
   homepage 'https://www.consul.io/intro/getting-started/ui.html'
   license :mpl

Casks/nomad.rb

@@ -4,6 +4,8 @@ cask 'nomad' do
 
   # hashicorp.com/nomad was verified as official when first introduced to the cask
   url "https://releases.hashicorp.com/nomad/#{version}/nomad_#{version}_darwin_amd64.zip"
+  appcast 'https://github.com/hashicorp/nomad/releases.atom',
+          checkpoint: '7dbb430f88706ed39867506dc3da084838475e27de7570f524a202b3f73fa4c1'
   name 'Nomad'
   homepage 'https://nomadproject.io/'
   license :mpl

Casks/otto.rb

@@ -4,6 +4,8 @@ cask 'otto' do
 
   # hashicorp.com is the official download host per the vendor homepage
   url "https://releases.hashicorp.com/otto/#{version}/otto_#{version}_darwin_amd64.zip"
+  appcast 'https://github.com/hashicorp/otto/releases.atom',
+          checkpoint: '046259c2cdb9af18491ccd60ad06023717ef958404b77a4845138e75cb053fe7'
   name 'Otto'
   homepage 'https://www.ottoproject.io/'
   license :mpl

Casks/packer.rb

@@ -4,6 +4,8 @@ cask 'packer' do
 
   # hashicorp.com is the official download host per the vendor homepage
   url "https://releases.hashicorp.com/packer/#{version}/packer_#{version}_darwin_amd64.zip"
+  appcast 'https://github.com/mitchellh/packer/releases.atom',
+          checkpoint: 'e5561e741b39748bb7f33a90122f974d19281d00ad0c768abb58294df01187fe'
   name 'Packer'
   homepage 'https://www.packer.io/'
   license :oss

Casks/serf.rb

@@ -4,6 +4,8 @@ cask 'serf' do
 
   # hashicorp.com/serf was verified as official when first introduced to the cask
   url "https://releases.hashicorp.com/serf/#{version}/serf_#{version}_darwin_amd64.zip"
+  appcast 'https://github.com/hashicorp/serf/releases.atom',
+          checkpoint: 'ddc3f79c2b3e97a00f88d514dda17428961eccefd74afeb8470a0e458af33c7d'
   name 'Serf'
   homepage 'https://www.serfdom.io/'
   license :mpl

Casks/vagrant.rb

@@ -4,6 +4,8 @@ cask 'vagrant' do
 
   # hashicorp.com/vagrant was verified as official when first introduced to the cask
   url "https://releases.hashicorp.com/vagrant/#{version}/vagrant_#{version}.dmg"
+  appcast 'https://github.com/mitchellh/vagrant/releases.atom',
+          checkpoint: '420b81d52032389f4159835fda75cd8d4d5cf0611ed7b238ba488ed2af3e9046'
   name 'Vagrant'
   homepage 'https://www.vagrantup.com/'
   license :mit

Casks/vault.rb

@@ -4,6 +4,8 @@ cask 'vault' do
 
   # hashicorp.com/vault was verified as official when first introduced to the cask
   url "https://releases.hashicorp.com/vault/#{version}/vault_#{version}_darwin_amd64.zip"
+  appcast 'https://github.com/hashicorp/vault/releases.atom',
+          checkpoint: '42046119b424a397ec33ae94799992d07609c3ac8f6362b843b8bf38c9e01ac5'
   name 'Vault'
   homepage 'https://www.vaultproject.io/'
   license :mpl