natural@2.1.5 - phonetics/soundex - Unterminated character class

SoundEx.process('`[foo]`')

```
natural/lib/natural/phonetics/soundex.js:72
    transformed = transformed.replace(new RegExp("^" + transform(token.charAt(0))), '');
                                      ^
SyntaxError: Invalid regular expression: /^[/: Unterminated character class
```