`Spond.update_events(uid...)` will modify or overwrite another event, if no event matching uid exists

[elliot-100]

Extracting specific bug from PR #134:

...a bug in update_events: the loop in

Spond/spond/spond.py

Lines 332 to 334 in bcb2b6d

	for event in self.events:
	if event["id"] == uid:
	break

will fall through, if no event matching uid exists, and proceed to modify or overwrite whatever event was last in the loop.

Refactoring the code to use self._get_entity(self._EVENT, uid) should ensure an error is raised when the uid is not matched, and prevent any event modification.

[elliot-100]

Fixed by PR #161