Fixes add_worklog started time
Fixes add_worklog started time

Bug reported through issue #369:
- Added .000+0000%z to the strftime conversion. Tested with my jira
instance and it now creates a worklog fine with the started parameter
set as a datetime object. It does not capture milliseconds, as they are
essentially all gettting rounded down.

dwmarshall/pycontribs-jira,pycontribs/jira,dwmarshall/pycontribs-jira,pycontribs/jira