Fix Travis CI build: use setuptools==60.9.0

Newer versions have at least one bug under old Python, as per
pypa/setuptools#3293

Author: mruffalo

.travis.yml

@@ -12,6 +12,7 @@ install:
   - cd ingest-validation-tools
   - pwd
   - git checkout v0.0.5
+  - pip install "setuptools==60.9.0"
   - pip install -r requirements.txt
 
   - cd ../ingest-validation-tests # Not sure if this is required, or if it resets between sections.