Update docs/language/learn-ql/javascript/type-tracking.rst

Co-Authored-By: jf205 <42464962+jf205@users.noreply.github.com>

Author: asger-semmle

docs/language/learn-ql/javascript/type-tracking.rst

@@ -347,7 +347,7 @@ all functions that flow into the ``once()`` call.
 Backwards type tracking is not too different from forwards type tracking. The differences are:
 
 - The ``TypeTracker`` parameter instead has type ``TypeBackTracker``.
-- The call to ``.track()`` is instead a call to ``.backtrack()``
+- The call to ``.track()`` is instead a call to ``.backtrack()``.
 - To ensure the initial value is a source node, a call to ``getALocalSource()`` is usually required.
 
 .. code-block:: ql