Invalid escape sequence in fireeye importer

```python
/vulnerablecode/vulnerabilities/importers/fireeye.py:115: SyntaxWarning: invalid escape sequence '\['
  markup_regex = "\[([^\[]+)]\(\s*(http[s]?://.+)\s*\)"
/vulnerablecode/vulnerabilities/pipelines/v2_importers/fireeye_importer_v2.py:157: SyntaxWarning: invalid escape sequence '\['
  markup_regex = "\[([^\[]+)]\(\s*(http[s]?://.+)\s*\)"
```