Allow os.date with no argument - fixes #91

[codecov[bot]]

Codecov Report

Base: 88.82% // Head: 87.75% // Decreases project coverage by -1.07% :warning:

Coverage data is based on head (3ca0f80) compared to base (0e5b284). Patch coverage: 57.14% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## lua5.4 #95 +/- ## ========================================== - Coverage 88.82% 87.75% -1.08% ========================================== Files 104 107 +3 Lines 11233 11472 +239 ========================================== + Hits 9978 10067 +89 - Misses 949 1086 +137 - Partials 306 319 +13 ``` | [Impacted Files](https://codecov.io/gh/arnodel/golua/pull/95?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Arnaud+Delobelle) | Coverage Δ | | |---|---|---| | [lib/oslib/oslib.go](https://codecov.io/gh/arnodel/golua/pull/95?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Arnaud+Delobelle#diff-bGliL29zbGliL29zbGliLmdv) | `38.32% <57.14%> (ø)` | | | [lib/oslib/clock.go](https://codecov.io/gh/arnodel/golua/pull/95?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Arnaud+Delobelle#diff-bGliL29zbGliL2Nsb2NrLmdv) | `0.00% <0.00%> (ø)` | | | [lib/oslib/clock\_windows.go](https://codecov.io/gh/arnodel/golua/pull/95?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Arnaud+Delobelle#diff-bGliL29zbGliL2Nsb2NrX3dpbmRvd3MuZ28=) | `28.57% <0.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Arnaud+Delobelle). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Arnaud+Delobelle)

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