*: vendor golint to prevent upstream changes from breaking the build

golint has updated or dropped support for old Go versions several times,
causing breaks in our build. Vendor it locally to prevent this.

Makefile

@@ -51,9 +51,9 @@ vet:
 fmt:
 	@./scripts/gofmt $(shell go list ./... | grep -v '/vendor/')
 
-lint:
+lint: bin/golint
 	@for package in $(shell go list ./... | grep -v '/vendor/' | grep -v '/api' | grep -v '/server/internal'); do \
-      golint -set_exit_status $$package $$i || exit 1; \
+      ./bin/golint -set_exit_status $$package $$i || exit 1; \
 	done
 
 .PHONY: docker-image
@@ -75,6 +75,9 @@ bin/protoc: scripts/get-protoc
 bin/protoc-gen-go:
 	@go install -v $(REPO_PATH)/vendor/github.com/golang/protobuf/protoc-gen-go
 
+bin/golint:
+	@go install -v $(REPO_PATH)/vendor/golang.org/x/lint/golint
+
 clean:
 	@rm -rf bin/