fix: setuptools for python 3.7

.travis.yml

@@ -20,7 +20,7 @@ matrix:
     dist: xenial
 services: mongodb
 before_install:
-  - pip install --upgrade pip setuptools
+  - if [[ $TRAVIS_PYTHON_VERSION == 3.7 ]]; then pip install "pip<22" setuptools; else pip install --upgrade pip setuptools; fi
 install:
   - if [[ $TRAVIS_PYTHON_VERSION == pypy* ]]; then pip install "tinydb<4"; fi
   - pip install "pymongo<4"