CI: Fixes for Go 1.13 (#11)

See also letsencrypt/gorepotemplate#7

.golangci.yaml

@@ -20,3 +20,4 @@ linters:
     - gocritic
     - gochecknoinits
     - gochecknoglobals
+    - typecheck # Go 1.13 incompatible pending new golangci-lint binary release

.travis.yml

@@ -1,14 +1,12 @@
 language: go
 go:
   - "stable"
-env:
-  - GO111MODULE=on
 
 # Override the base install phase so that the project can be installed using
 # `-mod=vendor` to use the vendored dependencies
 install:
   # Install `golangci-lint` using their installer script
-  - curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b $(go env GOPATH)/bin v1.13.2
+  - curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b $(go env GOPATH)/bin v1.17.1
   # Install `cover` and `goveralls` without `GO111MODULE` enabled so that we
   # don't download project dependencies and just put the tools in $GOPATH/bin
   - GO111MODULE=off go get golang.org/x/tools/cmd/cover
@@ -17,7 +15,6 @@ install:
 
 script:
   - set -e
-  - go mod download
   - golangci-lint run
   - go test -mod=vendor -v -race -covermode=atomic -coverprofile=coverage.out ./...
   - goveralls -coverprofile=coverage.out -service=travis-ci