remove uses of errors.Is, which requires go1.13

Commit 1bf832c6fec8a35a8c1d61e5fb14f5ce404197ef introduced the use of
`errors.Is`, which was added in [go1.13], but the `go.mod` was not
updated to reflect this, causing compile failures on go1.12:

    docker run -it --rm -v ./:/pflag -w /pflag golang:1.12 sh -c 'go test -v ./...'
    # github.com/spf13/pflag [github.com/spf13/pflag.test]
    ./flag.go:1190:7: undefined: errors.Is
    ./flag.go:1219:7: undefined: errors.Is
    ./bool_func_test.go:86:28: cannot use stdFSet (type *flag.FlagSet) as type BoolFuncFlagSet in argument to runCase:
        *flag.FlagSet does not implement BoolFuncFlagSet (missing BoolFunc method)
    ...

As the error that is tested will not be wrapped, we can omit the `errors.Is`,
and instead continue doing a straight comparison.

[go1.13]: https://pkg.go.dev/[email protected]#Is

Signed-off-by: Sebastiaan van Stijn <[email protected]>

0 files changed, 0 insertions, 0 deletions