event time accepts values greater than 23:59:59

[nus-se-bot]

Describe the bug Specifying the time for an event allows invalid values. eg larger than 23:59:59

To Reproduce Steps to reproduce the behavior:

1. addE n/careedrdd talk d/dcdompany info session v/com1 level2 s/2019-01-31 99:00:00 e/2019-01-31 14:00:00 l/important

Expected behavior It should return an invalid date/time command

Screenshots

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Reported by: @jeffgan96 Severity: Medium

_{[original: nus-cs2103-AY1819S2/pe-dry-run#219]}

[jwl1997]

bug fixed, thanks!