Add mips architecture support

[daixiang0]

Now golangci-lint does not support MIPS arch:

golangci/golangci-lint crit platform linux/mips64 is not supported.  Make sure this script is up-to-date and file request at https://github.com/golangci/golangci-lint/issues/new

I can do the porting and test if possible.

[daixiang0]

@tpounds mind have a look?

[ernado]

Probably it will be enough to add mips to .goreleaser.yml:builds.[0].goarch.

There are mips64, mips64le and their 32-bit versions, and I'm not sure what arch is needed exactly, so feel free to add a PR.