fix deprecation warning about get_cache()

Since Django 1.8 get_cache() is deprecated in favor of caches[].

src/authentic2_auth_fc/views.py

@@ -20,7 +20,7 @@ from django.utils.translation import ugettext as _
 from django.utils.http import is_safe_url, urlencode
 from django.conf import settings
 from django.core import signing
-from django.core.cache import InvalidCacheBackendError, get_cache
+from django.core.cache import InvalidCacheBackendError, caches
 from django.core.exceptions import PermissionDenied
 from django.core.urlresolvers import reverse
 from django.forms import Form
@@ -52,9 +52,9 @@ class LoggerMixin(object):
         super(LoggerMixin, *args, **kwargs)
 
 try:
-    cache = get_cache('fc')
+    cache = caches['fc']
 except InvalidCacheBackendError:
-    cache = get_cache('default')
+    cache = caches['default']
 
 
 CACHE_TIMEOUT = 60