Fixed naming of Vagrant boxes.

The boxes are now hosted in the Vagrant cloud and are thus named
differently.

cf.
hashicorp/vagrant#9897 (comment)

Vagrantfile

@@ -3,8 +3,7 @@
 
 Vagrant.configure('2') do |config|
   # See also: `script/vagrant-test`, `script/vagrant-test-all`
-  config.vm.box     = ENV['MAID_TARGET_BOX'] || 'precise64'
-  config.vm.box_url = 'http://files.vagrantup.com/precise64.box' if 'precise64' == config.vm.box
+  config.vm.box     = ENV['MAID_TARGET_BOX'] || 'hashicorp/precise64'
 
   config.vm.provider :virtualbox do |vb|
     # Maid has very low system requirements

script/vagrant-test-all

@@ -28,7 +28,7 @@
 # * [Vagrant Boxes List](http://www.vagrantbox.es/)
 # * [Contributing Guide](https://github.com/benjaminoakes/maid/wiki/Contributing)
 
-MAID_TARGET_BOX='precise32' MAID_TARGET_RUBY='1.9.3' script/vagrant-test
-MAID_TARGET_BOX='precise64' MAID_TARGET_RUBY='1.9.3' script/vagrant-test
+MAID_TARGET_BOX='hashicorp/precise32' MAID_TARGET_RUBY='1.9.3' script/vagrant-test
+MAID_TARGET_BOX='hashicorp/precise64' MAID_TARGET_RUBY='1.9.3' script/vagrant-test
 # TODO: Locate and add box for `saucy32`
 # TODO: Locate and add box for `saucy64`