updated changelog: added missing info on six dependency

Author: smarie

docs/changelog.md

@@ -3,6 +3,7 @@
 ### 1.8.0 - New fixtures for `pytest-harvest`
 
  - New fixtures `step_bag` and `cross_bag`, that may be used when `pytest-harvest` is installed. These fixtures are versions of `pytest-harvest`'s `results_bag` fixture that can be used with steps. Fixes [#49](https://github.com/smarie/python-pytest-steps/issues/49). PR [#46](https://github.com/smarie/python-pytest-steps/pull/46) by [`j-carson`](https://github.com/j-carson).
+ - `six` is not a dependency anymore.
 
 ### 1.7.3 - packaging improvements