Update CONFLUENCE_INSTALLFILE to 5.7
Update CONFLUENCE_INSTALLFILE to 5.7

This should fix https://github.com/gmacario/vagrant-atlassian/issues/49
Also fixing https://github.com/gmacario/vagrant-atlassian/issues/48

Signed-off-by: Gianpaolo Macario <f8885408b8c3d931b330bae3c3a28a3af912c463@gmail.com>

gmacario/vagrant-atlassian