Closes #91: WebDAV: Change requirement protocol

install/requirements.txt

 vobject==0.9.2
 waitress==0.8.9
 who-ldap==3.1.0
--e git+https://github.com/Nonolost/wsgidav.git@a5df223d5c66c252baa89ec5de8073f9f1494a8f#egg=wsgidav
+-e git+https://github.com/algoo/wsgidav.git@py3#egg=wsgidav
 zope.interface==4.1.3
 zope.sqlalchemy==0.7.6