Add millisecond format to date parsing

[PJSimon]

No description provided.

[boxcla]

Verified that @PJSimon has signed the CLA. Thanks for the pull request!

[coveralls]

Pull Request Test Coverage Report for Build 2077

• 9 of 11 (81.82%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.07%) to 65.306%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/java/com/box/sdk/BoxDateFormat.java	9	11	81.82%

Files with Coverage Reduction	New Missed Lines	%
src/main/java/com/box/sdk/BoxDateFormat.java	1	80.0%

Totals
Change from base Build 2075:	0.07%
Covered Lines:	5408
Relevant Lines:	8281

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💛 - Coveralls