support for older python versions

[fireba11]

There are several widely used distros that don't have python 3.9, and it doesn't seem to work with even 3.8 never mind even older.

On Ubuntu 18.04 with python 3.6.9 and
on ubuntu 20.04 with python 3.8.10

Starting scan of:/
Scanning for Vulnerabilities:
Traceback (most recent call last):
File "creosote.py", line 226, in
main()
File "creosote.py", line 206, in main
scan(directory)
File "creosote.py", line 50, in scan
analyzer = Analyzer(filename, text)
File "creosote.py", line 83, in init
self.visit(root)
File "/usr/lib/python3.6/ast.py", line 253, in visit
return visitor(node)
File "/usr/lib/python3.6/ast.py", line 261, in generic_visit
self.visit(item)
File "/usr/lib/python3.6/ast.py", line 253, in visit
return visitor(node)
File "/usr/lib/python3.6/ast.py", line 261, in generic_visit
self.visit(item)
File "/usr/lib/python3.6/ast.py", line 253, in visit
return visitor(node)
File "/usr/lib/python3.6/ast.py", line 261, in generic_visit
self.visit(item)
File "/usr/lib/python3.6/ast.py", line 253, in visit
return visitor(node)
File "/usr/lib/python3.6/ast.py", line 261, in generic_visit
self.visit(item)
File "/usr/lib/python3.6/ast.py", line 253, in visit
return visitor(node)
File "/usr/lib/python3.6/ast.py", line 263, in generic_visit
self.visit(value)
File "/usr/lib/python3.6/ast.py", line 253, in visit
return visitor(node)
File "/usr/lib/python3.6/ast.py", line 263, in generic_visit
self.visit(value)
File "/usr/lib/python3.6/ast.py", line 253, in visit
return visitor(node)
File "creosote.py", line 132, in visit_Attribute
if ".getmembers()" in ast.unparse(for_node.iter) and for_node.parent.body:
AttributeError: module 'ast' has no attribute 'unparse'

[papalii]

Same problem with Rocky Linux release 8.6 (Green Obsidian) and Python 3.6.8 (default, Sep 13 2022, 09:02:49)