Move several steps closer to python3 compatibility

Signed-off-by: Igor Ch <usrenmae@gmail.com>

compose/cli/command.py

@@ -25,7 +25,7 @@ class Command(DocoptCommand):
     def dispatch(self, *args, **kwargs):
         try:
             super(Command, self).dispatch(*args, **kwargs)
-        except SSLError, e:
+        except SSLError as e:
             raise errors.UserError('SSL error: %s' % e)
         except ConnectionError:
             if call_silently(['which', 'docker']) != 0:

compose/cli/log_printer.py

@@ -46,7 +46,7 @@ class LogPrinter(object):
             if monochrome:
                 color_fn = no_color
             else:
-                color_fn = color_fns.next()
+                color_fn = next(color_fns)
             generators.append(self._make_log_generator(container, color_fn))
 
         return generators