Use simplejson throughout

Let's use simplejson rather than json, for consistency.

synapse/api/errors.py

@@ -15,9 +15,10 @@
 
 """Contains exceptions and error codes."""
 
-import json
 import logging
 
+import simplejson as json
+
 logger = logging.getLogger(__name__)
 
 

synapse/handlers/identity.py

@@ -15,6 +15,11 @@
 # limitations under the License.
 
 """Utilities for interacting with Identity Servers"""
+
+import logging
+
+import simplejson as json
+
 from twisted.internet import defer
 
 from synapse.api.errors import (
@@ -24,9 +29,6 @@ from ._base import BaseHandler
 from synapse.util.async import run_on_reactor
 from synapse.api.errors import SynapseError, Codes
 
-import json
-import logging
-
 logger = logging.getLogger(__name__)
 
 

synapse/storage/schema/delta/14/upgrade_appservice_db.py

@@ -12,9 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import json
 import logging
 
+import simplejson as json
+
 logger = logging.getLogger(__name__)