fix libjs

Author: devsnek

src/engines/libjs.js

@@ -69,7 +69,7 @@ class LibJSInstaller extends Installer {
 
   async test() {
     const program = 'console.log("42")';
-    const output = '42';
+    const output = '"42"';
 
     assert.strictEqual(
       (await execa(this.binPath, ['-c', program])).stdout,