Remove govendor references

 - 'go mod verify' is not that useful and isn't equivalent to govendor status.
 - 'go mod tidy -v' does not return non-zero exit code when dependencies aren't tidy
 - We might add 'go mod tidy -check' at some point, when it becomes a thing.
   See golang/go#27005
   Until then it's better to keep provider setup aligned though.

.travis.yml

@@ -5,18 +5,18 @@ services:
 language: go
 go:
   - "1.11.x"
+env:
+  - GOFLAGS=-mod=vendor GO111MODULE=on
 
 install:
 # This script is used by the Travis build to install a cookie for
 # go.googlesource.com so rate limits are higher when using `go get` to fetch
 # packages that live there.
 # See: https://github.com/golang/go/issues/12933
 - bash scripts/gogetcookie.sh
-- go get github.com/kardianos/govendor
 
 script:
 - make test
-- make vendor-status
 - make vet
 - make website-test
 

GNUmakefile

@@ -7,18 +7,18 @@ export ACME_SERVER_URL ?= https://acme-staging-v02.api.letsencrypt.org/directory
 
 default: build
 
-build: fmtcheck vendor-status
+build: fmtcheck
 	go install
 
-test: fmtcheck vendor-status
+test: fmtcheck
 	go test -i $(TEST) || exit 1
 	echo $(TEST) | \
 		xargs -t -n4 go test $(TESTARGS) -timeout=30s -parallel=4
 
-testacc: fmtcheck vendor-status
+testacc: fmtcheck
 	TF_ACC=1 go test $(TEST) -v $(TESTARGS) -timeout 240m
 
-debugacc: fmtcheck vendor-status
+debugacc: fmtcheck
 	TF_ACC=1 dlv test $(TEST) -- -test.v $(TESTARGS)
 
 vet:
@@ -39,10 +39,6 @@ fmtcheck:
 errcheck:
 	@sh -c "'$(CURDIR)/scripts/errcheck.sh'"
 
-vendor-status:
-	go mod tidy -v
-	go mod verify
-
 test-compile:
 	@if [ "$(TEST)" = "./..." ]; then \
 		echo "ERROR: Set TEST to a specific package. For example,"; \
@@ -65,4 +61,4 @@ ifeq (,$(wildcard $(GOPATH)/src/$(WEBSITE_REPO)))
 endif
 	@$(MAKE) -C $(GOPATH)/src/$(WEBSITE_REPO) website-provider-test PROVIDER_PATH=$(shell pwd) PROVIDER_NAME=$(PKG_NAME)
 
-.PHONY: build test testacc vet fmt fmtcheck errcheck vendor-status test-compile website website-test
+.PHONY: build test testacc vet fmt fmtcheck errcheck test-compile website website-test