Update INSTALL.md

I changed pre-requisites to 4.4.5 as we found when I installed this on a 4.4.4 CiviCRM we encountered an error. The civiHR requires 4.4.5 or higher in order to get this commit https://github.com/civicrm/civicrm-core/commit/ab5fa8f252750f2e8c0854916371d02b61ecb5c0 which solved our problems