Support installing with the new go1.16 go install.
Changelog
022dccf Merge pull request #179 from dnephin/support-go-install-latest
badd934 Replace spf13/pflag with dnephin/pflag
c1e2e92 Merge pull request #178 from dnephin/go1.16-release
66df551 ci: use official release of go1.16
