stack/slapos.cfg: fix eggs version for python3.7

Werkzeug 3.0.0 is not compatible with Python3.7:

  File "/opt/slapos/eggs/werkzeug-3.0.0-py3.7.egg/werkzeug/serving.py",
line 76, in <module>
    t.Union["ssl.SSLContext", t.Tuple[str, t.Optional[str]],
t.Literal["adhoc"]]
AttributeError: module 'typing' has no attribute 'Literal

stack/slapos.cfg

@@ -353,8 +353,13 @@ zope.interface = 5.4.0
 zope.testing = 4.7
 zope.testrunner = 5.2
 
+# this is mostly needed for slapos-node
+# it can be removed when slapos-node uses current python3
 [versions:sys.version_info < (3,8)]
+Flask = 1.1.2
+MarkupSafe = 2.0.1
 typing-extensions = 4.7.1:whl
+Werkzeug = 2.0.2
 
 [versions:python2]
 attrs = 18.2.0