Fix use of non-existent time zone in fromDateTimeString()

[leftmostcat]

Timezone.localTimezone is the correct identifier here, not Timezone.floating. The version in trunk will succeed when tzid isn't set on the property (which, when we're defining a time zone, they shouldn't be), as we'll then fall back to Timezone.localTimezone when we instantiate the Time object. However, if tzid were set on the date prop, we could get some odd behavior.

[coveralls]

Pull Request Test Coverage Report for Build 4920724117

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.074%

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Totals
Change from base Build 4409613025:	0.0%
Covered Lines:	9271
Relevant Lines:	9438

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💛 - Coveralls