Add pins for wxPython.

When trying a pip install of all constraints, to gather all packages, I get errors on both Python 2 and 3.
Something is pulling in wxPython, and latest 4.2.0 cannot be installed on my Mac.
See various reports: https://github.com/wxWidgets/Phoenix/issues?q=is%3Aissue+is%3Aopen+attrdict

release/constraints.txt

@@ -398,6 +398,8 @@ webencodings==0.5.1
 wheel==0.37.1
 wmctrl==0.3
 wrapt==1.12.1
+wxPython==4.0.7.post2; python_version < "3.0"
+wxPython==4.1.1; python_version >= "3.0"
 z3c.autoinclude==0.4.1
 z3c.batching==2.2
 z3c.blobfile==0.1.5

versions.cfg

@@ -379,6 +379,7 @@ jeepney = 0.4.3
 feedparser = 6.0.8
 sgmllib3k = 1.0.0
 typing =
+wxPython = 4.1.1
 
 [versions:python27]
 cachecontrol = 0.12.6
@@ -402,6 +403,7 @@ trollius = 2.2.post1
 twine = 1.15.0
 typing = 3.10.0.0
 watchdog = 0.10.6
+wxPython = 4.0.7.post2
 
 # BBB only packages (to be removed with Plone 5.3 or 6.0 and in 5.2 on Python 3.6+
 plone.app.controlpanel                = 4.0.1