Update alarm.py

In case of Choice 1 the previous code would play alarm on wrong time. For e.g. current time is 03:40 and users sets alarm for after 150 minutes so it should play alarm on 06:10 but code would play at 5:10 itself.
I have edited the code for this condition as well.
Merge pull request #43 from gaurav-91/patch-1

Update alarm.py