Fix SyntaxError: invalid syntax - comma.

  File "/var/jenkins/workspace/openstack-tempest_on-slave_testing/tempest/tempest/services/object_storage/account_client.py", line 36
    headers = {"X-Storage-Token", self.token}
                                ^
SyntaxError: invalid syntax

Change-Id: I850aba75a28edfd2990accadfb0f3e7115eba864
diff --git a/tempest/services/object_storage/account_client.py b/tempest/services/object_storage/account_client.py
index ade94d4..2a686f6 100644
--- a/tempest/services/object_storage/account_client.py
+++ b/tempest/services/object_storage/account_client.py
@@ -33,7 +33,7 @@
         Returns all account metadata headers
         """
 
-        headers = {"X-Storage-Token", self.token}
+        headers = {"X-Storage-Token": self.token}
         resp, body = self.head('', headers=headers)
         return resp, body