make vendor: always check for latest vndr

@baude and I have recently debugged a `make vendor` issue, where
different versions of `vndr` leave slightly different states behind.
This ultimately leads to inconsistencies with the CI, which always
fetches the latest version.

To avoid such issues in the future, always use the latest version of
`vndr` by checking for new versions of it prior to execution.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

Makefile

@@ -289,7 +289,7 @@ uninstall:
 install.tools: .install.gitvalidation .install.gometalinter .install.md2man .install.ginkgo ## Install needed tools
 
 .install.vndr: .gopathok
-	$(GO) get github.com/LK4D4/vndr
+	$(GO) get -u github.com/LK4D4/vndr
 
 .install.ginkgo: .gopathok
 	if [ ! -x "$(GOBIN)/ginkgo" ]; then \
@@ -348,10 +348,11 @@ build-all-new-commits:
 	# Validate that all the commits build on top of $(GIT_BASE_BRANCH)
 	git rebase $(GIT_BASE_BRANCH) -x make
 
-vendor:
-	vndr -whitelist "github.com/varlink/go"  \
-	     -whitelist "github.com/onsi/ginkgo" \
-	     -whitelist "github.com/onsi/gomega"
+vendor: .install.vndr
+	$(GOPATH)/bin/vndr \
+		-whitelist "github.com/varlink/go"  \
+		-whitelist "github.com/onsi/ginkgo" \
+		-whitelist "github.com/onsi/gomega"
 
 .PHONY: \
 	.gopathok \