PendingDeprecationWarning at pycodegen

[paxet]

A PendingDeprecationWarning can be seen at:

pony/thirdparty/compiler/pycodegen.py:4: PendingDeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
import imp

There is no hurry for the update, but must be considered.

[kozlovsky]

Thanks for the patch