Fail the command on any non-zero value

This check makes more sense and the previous one was copied verbatim from the aws provider provided as reference by Hashicorp

Author: kilokahn

GNUmakefile

@@ -35,7 +35,7 @@ testacc: fmtcheck gomodenv
 
 vet:
 	@echo "go vet ."
-	@go vet $$(go list ./... | grep -v vendor/) ; if [ $$? -eq 1 ]; then \
+	@go vet $$(go list ./... | grep -v vendor/) ; if [ $$? -ne 0 ]; then \
 		echo ""; \
 		echo "Vet found suspicious constructs. Please check the reported constructs"; \
 		echo "and fix them if necessary before submitting the code for review."; \