Update changeStream.txt

Adds a missing closing bracket reported in Slack via feedback.

Author: terakilobyte

source/usage-examples/changeStream.txt

@@ -19,7 +19,7 @@ In the example below, the ``$match`` stage will match all change event documents
 
 .. code-block:: javascript
 
-   const pipeline = [ { $match: { runtime: { $lt: 15 } } ];
+   const pipeline = [ { $match: { runtime: { $lt: 15 } } } ];
    const changeStream = collection.watch(pipeline);
 
 The ``watch()`` method accepts an ``options`` object as the second parameter. Refer to the links at the end of this