nit(spec): SHOULD BE => SHOULD be

[bassosimone]

This change is 

[coveralls]

Pull Request Test Coverage Report for Build 1558

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 7 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.3%) to 81.768%

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Files with Coverage Reduction	New Missed Lines	%
ndt7/measurer/measurer.go	2	89.47%
ndt7/upload/sender/sender.go	5	65.91%
<!--	Total:	7		-->

Totals
Change from base Build 1557:	0.3%
Covered Lines:	1767
Relevant Lines:	2161

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💛 - Coveralls

[robertodauria]

It looks like one of the two (identical) builds on Travis has stalled, and the other one succeeded.