Fix ’make test’ when GOPATH contains multiple paths (#658)

Makefile

@@ -155,7 +155,7 @@ ifeq "$(BUILD_IN_DOCKER)" "true"
 	$(DOCKER) run -v $(PWD):/go/src/github.com/cloudnativelabs/kube-router -w /go/src/github.com/cloudnativelabs/kube-router $(DOCKER_BUILD_IMAGE) \
 			sh -c 'apk add --no-cache git build-base && go get github.com/matryer/moq && go generate -v $(*).go'
 else
-	@test -x $(GOPATH)/bin/moq && exit 0; echo "ERROR: 'moq' tool is needed to update mock test files, install it with: \ngo get github.com/matryer/moq\n"; exit 1
+	@test -x $(lastword $(subst :, ,$(GOPATH)))/bin/moq && exit 0; echo "ERROR: 'moq' tool is needed to update mock test files, install it with: \ngo get github.com/matryer/moq\n"; exit 1
 	go generate -v $(*).go
 endif