Bump async transport default batch size to 200 (#385)

Author: c24t

opencensus/common/transports/async_.py

@@ -23,7 +23,7 @@
 from opencensus.common.transports import base
 
 _DEFAULT_GRACE_PERIOD = 5.0  # Seconds
-_DEFAULT_MAX_BATCH_SIZE = 10
+_DEFAULT_MAX_BATCH_SIZE = 200
 _WAIT_PERIOD = 60.0  # Seconds
 _WORKER_THREAD_NAME = 'opencensus.common.Worker'
 _WORKER_TERMINATOR = object()