Bump python-rapidjson from 1.6 to 1.8

Bumps [python-rapidjson](https://github.com/python-rapidjson/python-rapidjson) from 1.6 to 1.8.
- [Release notes](https://github.com/python-rapidjson/python-rapidjson/releases)
- [Changelog](https://github.com/python-rapidjson/python-rapidjson/blob/master/CHANGES.rst)
- [Commits](https://github.com/python-rapidjson/python-rapidjson/compare/v1.6...v1.8)

---
updated-dependencies:
- dependency-name: python-rapidjson
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -26,7 +26,7 @@ joblib==1.1.0
 py_find_1st==1.1.5
 
 # Load ticker files 30% faster
-python-rapidjson==1.6
+python-rapidjson==1.8
 # Properly format api responses
 orjson==3.7.7