fix: use govulncheck -scan=module for library CI (#19)

Libraries should scan dependencies, not stdlib — the stdlib version
is the consumer's choice. -scan=module checks only go.mod deps.

Author: ankurs

Makefile

@@ -10,7 +10,7 @@ doc:
 
 lint:
 	go tool golangci-lint run
-	go tool govulncheck ./...
+	go tool govulncheck -scan=module
 
 bench:
 	go test -run=^$$ -bench=. -benchmem ./...