Increase memory of Vagrant, fixes #601 hopefully

Vagrantfile

@@ -1,6 +1,9 @@
 Vagrant.configure(2) do |config|
   config.vm.box = "ubuntu/trusty64"
   config.vm.network :forwarded_port, guest: 4567, host: 4567
+  config.vm.provider "virtualbox" do |vb|
+    vb.memory = "2048"
+  end
 
   config.vm.provision "bootstrap",
     type: "shell",
@@ -38,4 +41,4 @@ Vagrant.configure(2) do |config|
       cd /vagrant
       bundle exec middleman server --watcher-force-polling --watcher-latency=1 &> ~/middleman.log &
     SHELL
-end
+end