Update pre-install.sh

centos/pre-install.sh

@@ -5,3 +5,6 @@ yum install git
 
 #get the install script
 cd /usr/src && git clone https://github.com/fusionpbx/fusionpbx-install.sh.git
+
+#change the working directory
+cd /usr/src/fusionpbx-install.sh/centos