py-uncompyle6: updated to 3.7.4

3.7.4:
Fragment parsing was borked. This means deparsing in trepan2/trepan3k was broken
3.7+: narrow precedence for call tatement
del_stmt -> delete to better match Python AST
3.8+ Add another forelsestmt (found only in a loop)
3.8+ Add precedence on walrus operator
More files blackened
bump min xdis version

3.7.3:
Mostly small miscellaneous bug fixes
__doc__ = DocDescr() from test_descr.py was getting confused as a docstring.
detect 2.7 exchandler range better
Add for .. else reduction checks on 2.6 and before
Add reduce check for 2.7 augmented assign
Add VERSION in a pydoc-friendly way

3.7.2:
Use newer xdis
Docstrings (again) which were broken again on earlier Python
Fix 2.6 and 2.7 decompilation bug in handling "list if" comprehensions

(adam)