Update event_generator.py Typo Error

Found the small type error while reading the code.

Author: RajuGujjalapati

opcua/server/event_generator.py

@@ -15,7 +15,7 @@ class EventGenerator(object):
     """
     Create an event based on an event type. Per default is BaseEventType used.
     Object members are dynamically created from the base event type and send to
-    client when evebt is triggered (see example code in source)
+    client when event is triggered (see example code in source)
 
     Arguments to constructor are: