EAGLESIX-2651: Accumulator: fix misleading comment

lib/pipeline/accumulators/Accumulator.js

@@ -1,7 +1,7 @@
 "use strict";
 
 /**
- * A base class for all pipeline accumulators. Uses NaryExpression as a base class.
+ * A base class for all pipeline accumulators.
  * @class Accumulator
  * @namespace mungedb-aggregate.pipeline.accumulators
  * @module mungedb-aggregate