Skip gccolect test for python < 3

Signed-off-by: Krukov Dima <glebov.ru@gmail.com>

Author: Krukov

prometheus_client/gc_collector.py

@@ -7,9 +7,9 @@
 import time
 from collections import defaultdict
 
+from .metrics import Histogram
 from .metrics_core import HistogramMetricFamily
 from .registry import REGISTRY
-from .metrics import Histogram
 from .utils import INF
 
 

tests/test_gc_collector.py

@@ -1,11 +1,13 @@
 from __future__ import unicode_literals
 
 import gc
+import sys
 import unittest
 
 from prometheus_client import CollectorRegistry, GCCollector
 
 
+@unittest.skipIf(sys.version_info < (3, ), "Test requires Python 3.+")
 class TestGCCollector(unittest.TestCase):
     def setUp(self):
         gc.disable()