Fixed tests on Go 1.16 / gotip

[oxisto]

• Fixed a stringintconv issue. This made the tests fail in Go 1.16 and above
• Fixed an issue with the deprecated go lint on Go 1.16

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This change is 

[oxisto]

Strange... while this fixes the tests on Go 1.16 (and above - tested with go tip). The gotip travis environment still fails with weird go.sum errors, which I cannot reproduce.

Update: It looks like the culprit is the go get -u golang.org/x/lint/golint line, this behaves differently on 1.13 and 1.16+. In recent versions of Go, this will add additional entries to the go.mod file and thus, it will complain that the go.sum entries are not there.

Update 2: Switching to go vet on go tip (in non-fail mode) and the tests run, hooray.