zodburi: v↑ to 3.0.0 for python3

A new version of zodburi has been released [1] that
removes Python2 compatibility shims [2] and is therefore
needed to successfully run 'wendelin.core' tests with python3 [3].

Suggested by @kirr.

[1] https://pypi.org/project/zodburi/3.0.0/
[2] https://github.com/Pylons/zodburi/commit/a00fea755
[3] wendelin.core!35

/reviewed-by @kirr @jerome
/reviewed-on !1745

stack/slapos.cfg

@@ -417,7 +417,7 @@ ZConfig = 3.6.1
 zdaemon = 4.2.0
 zeroconf = 0.62.0:whl
 zipp = 3.12.0:whl
-zodburi = 2.5.0
+zodburi = 3.0.0
 zope.event = 5.0
 zope.exceptions = 5.2
 zope.interface = 7.1.1
@@ -501,6 +501,7 @@ websocket-client = 0.59.0
 Werkzeug = 1.0.1
 widgetsnbextension = 2.0.0
 zipp = 1.2.0:whl
+zodburi = 2.5.0
 zope.event = 4.6.0
 zope.exceptions = 4.6
 zope.interface = 5.5.2