generate error

on ML 10.8.2

```
$hexo generate
Loading.

/usr/local/lib/node_modules/hexo/node_modules/yamljs/bin/yaml.js:1219
                throw new YamlParseException('Unable to parse.', this.getRealCurrentLineNb
                  ^
YamlParseException: Unable to parse.
```

I just updated to 0.5.5. it's OK on 0.5.4 and I didn't make changes on _config.yml
