Add google.gax to default ignore list

google.gax depends on time.time() for communicating with external
systems. This is supposed to fix issues similar to
googleapis/google-cloud-python#3284

freezegun/api.py

@@ -520,6 +520,7 @@ def freeze_time(time_to_freeze=None, tz_offset=0, ignore=None, tick=False):
         ignore = []
     ignore.append('six.moves')
     ignore.append('django.utils.six.moves')
+    ignore.append('google.gax')
     ignore.append('threading')
     ignore.append('Queue')
     return _freeze_time(time_to_freeze, tz_offset, ignore, tick)