ci: update goreleaser install URL. (zmap#429)

The upstream project README[0] is using a different URL now and in my
tests the old URL has an HTTPS subject common name mismatch preventing
installation from succeeding and breaking the `make code-lint` phase of
integration tests.

[0]: https://github.com/golangci/golangci-lint#install

.travis.yml

@@ -7,7 +7,7 @@ go:
 
 install:
  # Install `golangci-lint` using the installer script
- - curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b $(go env GOPATH)/bin v1.21.0
+ - curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.21.0
 
 script:
  # Fast-fail on non-zero exit codes