Fix common typo, occured should be occurred

src/sugar3/graphics/alert.py

@@ -246,7 +246,7 @@ class Alert(Gtk.EventBox):
         Emitting response when we have a result
 
         A result can be that a user has clicked a button or
-        a timeout has occured, the id identifies the button
+        a timeout has occurred, the id identifies the button
         that has been clicked and -1 for a timeout
         """
         self.emit('response', response_id)

src/sugar3/logger.py

@@ -240,7 +240,7 @@ def trace(logger=None, logger_name=None, skip_args=None, skip_kwargs=None,
         try:
             res = f(*args, **kwargs)
         except:
-            trace_logger.exception("Exception occured in %s" % f.__name__)
+            trace_logger.exception("Exception occurred in %s" % f.__name__)
             raise
 
         trace_logger.log(TRACE, "%s(%s) returned %s", f.__name__,

src/sugar3/util.py

@@ -336,7 +336,7 @@ def _cleanup_temp_files():
             os.unlink(path)
         except:
             # pylint: disable=W0702
-            logging.exception('Exception occured in _cleanup_temp_files')
+            logging.exception('Exception occurred in _cleanup_temp_files')
 
 atexit.register(_cleanup_temp_files)