Update pre-install.sh

debian/pre-install.sh

@@ -8,3 +8,6 @@ apt-get install -y --force-yes 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/debian