Fix tag key for excludeFastQueryThresholdMs

[naveedyahyazadeh]

Original PR #112 used the incorrect tag key, this PR corrects that. Any span tagged with sampling.priority=0 will not be reported.

[coveralls]

Pull Request Test Coverage Report for Build 356

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 51.635%

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Totals
Change from base Build 355:	0.0%
Covered Lines:	537
Relevant Lines:	1040

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💛 - Coveralls

[mehta-ankit]

FYI @malafeev

[naveedyahyazadeh]

Thank you for merging, can you also release a new tag?

[malafeev]

it's released