indentation fix

Author: rustagir

source/aggregation/agg-exp-ops.txt

@@ -417,7 +417,7 @@ The following code shows the pipeline for this aggregation:
 
    To improve readability, the previous example assigns intermediary values to
    the ``totalSeats`` and ``isAvailable`` variables. If you don't assign
-  these intermediary values to variables, the code still produces
+   these intermediary values to variables, the code still produces
    equivalent results.
 
 The following code provides an equivalent aggregation pipeline in