fix(core): use getfullargspec when available

Fixes #25

Author: rubik

mando/core.py

@@ -5,6 +5,10 @@
 import sys
 import inspect
 import argparse
+try:
+    getfullargspec = inspect.getfullargspec
+except AttributeError:
+    getfullargspec = inspect.getargspec
 try:
     from itertools import izip_longest
 except ImportError:  # pragma: no cover
@@ -86,7 +90,7 @@ def _generate_command(self, func, name=None, doctype='rest',
             one is ``func.__name__``.'''
         func_name = func.__name__
         name = func_name if name is None else name
-        argspec = inspect.getargspec(func)
+        argspec = getfullargspec(func)
         self._argspecs[func_name] = argspec
         argz = izip_longest(reversed(argspec.args),
                             reversed(argspec.defaults or []),