Update monitoring.rst

Author: Yuki Kobayashi

Doc/c-api/monitoring.rst

@@ -194,5 +194,5 @@ would typically correspond to a python function.
 
 .. c:function:: int PY_MONITORING_IS_INSTRUMENTED_EVENT(uint8_t ev)
 
-   Return true if the event corresponding to event ID *ev* is
+   Return true if the event corresponding to the event ID *ev* is
    a :ref:`local event <monitoring-event-local>`.