Use inspect.getargspec() for PyPy3

PyPy3 is still using `inspect.getargspec()`, not `inspect.signature()`.

praw/decorators.py

@@ -48,8 +48,8 @@ def alias_function(function, class_name):
     """
     @wraps(function)
     def wrapped(self, *args, **kwargs):
-        if six.PY3:
-            # Python3 uses inspect.signature(), not inspect.getargspec()
+        if six.PY3 and not hasattr(sys, 'pypy_version_info'):
+            # CPython3 uses inspect.signature(), not inspect.getargspec()
             # see #551 and #541 for more info
             func_items = inspect.signature(function).parameters.items()
             func_args = [name for name, param in func_items
@@ -171,8 +171,8 @@ def require_captcha(function, *args, **kwargs):
                 # *args currently contains a None where the captcha answer
                 # needs to go. If we put the captcha in the **kwargs,
                 # we get a TypeError for having two values of the same param.
-                if six.PY3:
-                    # Python3 uses inspect.signature(), not
+                if six.PY3 and not hasattr(sys, 'pypy_version_info'):
+                    # CPython3 uses inspect.signature(), not
                     # inspect.getargspec() see #551 and #541 for more info
                     func_items = inspect.signature(function)
                     func_items = func_items.parameters.items()