Copy edits for typos

Signed-off-by: kay <kay.kim@10gen.com>

Author: epc

source/release-notes/3.1-dev-series-reference.txt

@@ -39,7 +39,7 @@ aggregation framework:
 
       { $sample: { size: <positive integer> } }
 
-   For example, the following aggregation operaton randomly selects
+   For example, the following aggregation operation randomly selects
    ``5`` documents from the collection:
 
    .. code-block:: javascript

source/release-notes/3.1-dev-series.txt

@@ -164,7 +164,7 @@ Partial indexes offer a more expressive mechanism than
 :doc:`/core/index-sparse` indexes to determine which documents are
 indexed.
 
-Sparse indexes selects documents to index *soley* based on the
+Sparse indexes selects documents to index *solely* based on the
 existence of the indexed field, or for compound indexes, the existence
 the indexed fields.
 
@@ -551,8 +551,8 @@ New Aggregation Array Operators
               }
           }
 
-General Enhacements
-~~~~~~~~~~~~~~~~~~~
+General Enhancements
+~~~~~~~~~~~~~~~~~~~~
 
 ``$project`` New Arrays
 ```````````````````````