Fix spurious character in code example.

Author: Max Schaefer

javascript/ql/src/Security/CWE-078/examples/indirect-command-injection.js

@@ -2,4 +2,4 @@ var cp = require("child_process");
 
 const args = process.argv.slice(2);
 const script = path.join(__dirname, 'bin', 'main.js');
-cp.execSync(`node ${script} ${args.join(' ')}"`); // BAD
+cp.execSync(`node ${script} ${args.join(' ')}`); // BAD