Fixes #110: Update lamp-infrastructure example to use CentOS 7.

Author: geerlingguy

lamp-infrastructure/Vagrantfile

@@ -3,7 +3,7 @@
 
 Vagrant.configure("2") do |config|
   # Base VM OS configuration.
-  config.vm.box = "geerlingguy/centos6"
+  config.vm.box = "geerlingguy/centos7"
   config.ssh.insert_key = false
   config.vm.synced_folder '.', '/vagrant', disabled: true