fix(rubocop): add fixes using rubocop --safe-auto-correct

Vagrantfile

@@ -1,24 +1,24 @@
+# frozen_string_literal: true
+
 # -*- mode: ruby -*-
 # vi: set ft=ruby :
 
 # Vagrantfile API/syntax version. Don't touch unless you know what you're doing!
-VAGRANTFILE_API_VERSION = "2"
+VAGRANTFILE_API_VERSION = '2'
 
 Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
-  config.vm.box = "ubuntu/trusty64"
-  config.vm.hostname = "salt"
-  config.vm.synced_folder "./", "/srv/salt", id: "vagrant-root"
+  config.vm.box = 'ubuntu/trusty64'
+  config.vm.hostname = 'salt'
+  config.vm.synced_folder './', '/srv/salt', id: 'vagrant-root'
 
   config.ssh.forward_agent = true
 
   config.vm.provider :virtualbox do |vb|
     # Use VBoxManage to customize the VM. For example to change memory:
-    vb.customize ["modifyvm", :id, "--memory", "1024"]
-  end
-  if Vagrant.has_plugin?("vagrant-cachier")
-    config.cache.scope = :box
+    vb.customize ['modifyvm', :id, '--memory', '1024']
   end
+  config.cache.scope = :box if Vagrant.has_plugin?('vagrant-cachier')
 
   # Set up salt-master and minion
-  config.vm.provision "shell", path: "dev/setup-salt.sh"
+  config.vm.provision 'shell', path: 'dev/setup-salt.sh'
 end