Modified for the fatal errors on a staticcheck verification.

[timakin]

Overview

With staticcheck command, the fatal errors on context_test appears on a console.

$ staticcheck
context_test.go:25:2: the goroutine calls T.Fatal, which must be called in the same goroutine as the test (SA2002)
context_test.go:105:2: the goroutine calls T.Fatal, which must be called in the same goroutine as the test (SA2002)

So changed not to use t.Fatal as fatal case of goroutine

Reference

https://github.com/prometheus/node_exporter/pull/439/files

[coveralls]

Coverage remained the same at 90.0% when pulling d827531 on timakin:fix/staticcheck-fatal into 66e76ef on Code-Hex:master.

[Code-Hex]

@timakin Thanks!!