fix support of unquoted value on time criteria

[fifthaxe]

influxql permits to set an unquoted string for a timestamp :
time >= 12ms

this PR adds support to this case

[coveralls]

Pull Request Test Coverage Report for Build 71

• 2 of 6 (33.33%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-1.2%) to 98.758%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
query_builder.go	2	6	33.33%

Totals
Change from base Build 65:	-1.2%
Covered Lines:	318
Relevant Lines:	322

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💛 - Coveralls

[benjamin658]

Thanks for your contribution, it would be great to add unit test on it, after the test passed, I will merge the PR, thanks again!