rate limiter proposed changes

lib/datadog/tracing/sampling/rate_limiter.rb

@@ -62,7 +62,7 @@ def initialize(rate, max_tokens = rate)
         # the tokens from the bucket.
         #
         # @return [Boolean] +true+ if message conforms with current bucket limit
-        def allow?(size)
+        def allow?(size = 1)
           allowed = should_allow?(size)
           update_rate_counts(allowed)
           allowed