Fixed time format

In Time Server task there's a typo in date format. Original quote:

Your server should listen to TCP connections on port 8000. For each
connection you must write the current date & time in the format:

  YYYY-MM-DD HH:MM
I think that time format should look like YYYY-MM-DD hh:mm. Especially it is important for minutes since minutes and months has similar format literals.
Merge pull request #36 from franza/master

Fixed time format for Time Server task