Fix inspect.getargspec deprecation warning in Python 3

[jhlegarreta]

The USE_PRE=1 builds are failing among others because the

DeprecationWarning: inspect.getargspec() is deprecated, use inspect.signature() instead
   specs = inspect.getargspec(fnc)

deprecation warning is being displayed due to the use of Python 3.

[jhlegarreta]

I'm looking into this. Would using

try: #Python3
    specs = inspect.signature(fnc)
except AttributeError: # Python2
   specs = inspect.getargspec(fnc)

solve the issue?

I've seen that others suggest using inspect.getfullargspec(), which seems to be fine:
https://docs.python.org/3/library/inspect.html

[naveenkumarmarri]

I've raised PR #1413 for this issue, can someone review it?

[jhlegarreta]

@skoudoro The corresponding card in the dipy 0.14.0 card can be marked as WIP.

[skoudoro]

Thanks for pointing that @jhlegarreta

[skoudoro]

#1413 is merged and card updated, you can close this issue @jhlegarreta.