[typo] miss <

https://gyp.gsrc.io/docs/InputFormatReference.md#variables-and-conditionals-command-expansions-example

```python
{
  'sources': [
    '!(echo filename with space.cc)',
  ],
  'libraries': [
    '!@(pkg-config --libs-only-l apr-1)',
  ],
}
```

Miss `<` before `!`.