grammar tweak

Author: Cladis

source/aggregation.txt

@@ -10,7 +10,7 @@ Aggregation
    :depth: 1
    :class: singlecol
 
-Aggregations operations process data records and return computed
+Aggregation operations process data records and return computed
 results. Aggregation operations group values from multiple documents
 together, and can perform a variety of operations on the grouped data
 to return a single result. MongoDB provides three ways to perform