fixed python version numbers
language: python
python:
- - "3.6.13"
- - "3.7.10"
- - "3.8.8"
- - "3.9.2"
- - "3.10"
+ - "3.6"
+ - "3.7"
+ - "3.8"
+ - "3.9"
+ - "3.10-dev"
install:
- pip install coveralls
- pip install tox
