support multiple files

Author: pathywang

implement-shell-tools/cat/cat.js

@@ -1,7 +1,8 @@
 const fs = require("fs");
 
-const filename = process.argv[2];
+const files = process.argv.slice(2);
 
-const content = fs.readFileSync(filename, "utf8");
-
-process.stdout.write(content);
+for (const file of files) {
+  const content = fs.readFileSync(file, "utf8");
+  process.stdout.write(content);
+}